text:
Why is Royal Flush ever listed separately from Straight Flush?
Many sources explicitly list Royal Flush as the highest poker hand (example). This seems unnecessary - it's the highest hand anyway as the highest Straight Flush. When presenting a ruleset, unnecessary is harmful (e.g. it gives new players more to remember). So is there a good historical or game-mechanics reason why we often treat the Royal Flush as a special case?
ADDENDUM: Several answers have pointed out that video poker pays out more for royal flush than other straight flushes. Could this be the historical origin I'm looking for? While the term "royal flush" appears in dictionaries long before video poker existed, no one has yet provided evidence that the silly presentation of royal flush as the highest hand in a full ranking of hands existed before video poker.

I post this question because I just had to disabuse someone of the idea that Four of a Kind came between Royal Flush and Straight Flush in Texas Holdem. This wouldn't have been needed if they'd never heard the words "Royal Flush"...

I edited your question to make the links readable. Feel free to further modify those links, but please don't make every other letter of a word a separate link.

I wouldn't be surprised if it was to emphasize the distinction between royalty and the plebes.

By the way, we have a Stack Exchange dedicated to Poker. I'm not totally sure what differentiates it from this site, or whether you would get a better answer there, but I thought I should mention it.

@Rainbolt: I didn't realize that; thanks! I've now posted it there as well.

So far on Poker SE I've attracted only one responder who seems both hostile and wrong. I think I'll stick with this community :)

There are a number of different hands that have a specific name. For example, A-2-3-4-5 is called a Wheel. The Royal Flush obviously gets its name from being the highest hand, and specifically having royalty in it (although one could argue so does a King high.)
As for the mistake of ranking of Straight Flush being lower than 4 of a kind, this is easily dispelled by looking at the math behind them. There exist only 40 straight flushes (of which 4 are Royal) and there are 624 unique hands that rank as four-of-a-kind.
One reason for it persisting would be in Video Poker where a Royal Flush tends to pay out significantly higher than the other Straight Flushes. This doesn't answer the question about how it managed to still exist before Video Poker was around, though.
I have had it conveyed to me recently that it's listed separately potentially due to wild-cards and how they affect the math - that perhaps a straight flush is not as difficult to acquire anymore where a Royal flush is. However I have not had an opportunity to run the math on it. I would welcome an addendum if someone does.

Do we care about card order for four-of-a-kind? It seems like there should only be 13 four-of-a-kinds.

I think he's talking about the number of hands that contain a four-of-a-kind. Each one also contains any one of the other 48 cards.

+1 for the bit about Video Poker, though as you point out there's a rationale that predates that and I'd love to hear it

This may not be suitable for an answer, but rather a hypothesis: Since Royal flushes are the highest hand, and are incredibly rare, they are memorable. Often people try to remember how many royal flushes they have gotten, which would be dulled if the royal flush was lumped with the straight flush.

Well this still isn't a complete answer, but my bounty did not attract a better one so it's yours.

In modern times (since 1980), this is likely because a Royal Flush pays substantially higher in video poker than a Straight Flush.  While payouts vary by machine, it's common for a Royal Flush to pay 800 - 1000 times the stake, where a (non-royal) Straight Flush only pays in 40 - 90 times the stake.
For player-on-player poker variants, a Royal Flush is not actually a different hand category from a Straight Flush, and many hand ranking lists (such as Wikipedia's) do not list it separately.
Poker is full of slang; there are an especially high number of poker terms for various "best hands".  The best hand possible in a particular situation (such as given a set of community cards) is kowns as "the nuts".  A pair of aces as hole cards in Texas Hold'em is the statistically best pre-flop hand, and so has a whole pile of nicknames (Rockets, American Airlines, Bullets, etc.).  An Ace through 5 straight is the best hand in some variants of lowball poker, and so has picked up the nickname the "Wheel".  Naturally, poker has a nickname for the best hand in the game as well, i.e. the Royal Flush.
Merriam-Webster lists the term Royal Flush as originating around 1868, but doesn't list a source.  However, it is worth noting that the term "Royal Flush" is prevalent enough to have made it into Merriam-Webster, where terms like "wheel" or "rockets" are not.  Given this, I would speculate that some hand orderings list Royal Flush as a separate hand category from a Straight Flush to prevent confusion on behalf of the players who are aware of the Royal Flush as a poker hand (and thus expecting it to be listed in a hand ordering).

Yeah, I'm not at all surprised that the term "royal flush" exists; the issue is just that it frequently unnecessarily appears in the hand rankings. For comparison, wouldn't you find it really weird to see a hand ranking that went "... flush > straight > wheel > three of a kind > ..."? even though this actually makes more sense than including royal flush, since aces acting as the low card in a straight is a special case that's worth pointing out explicitly, unlike the royal flush which is not truly a special case.

@BenjaminCosman There is a substantial difference in prevalence between the terms Royal Flush and Wheel.  You will notice that Royal Flush appears in Miriam Webster where Wheel (in the Poker sense) does not.

If a term is in common usage (so much so that it's actually in the dictionary) then it makes a lot of sense that it should be called out in the rules.  Otherwise you have to deal with the endless "Yes, but where is the 'royal' flush?"  questions.

As mentioned below my original post, a couple times I've seen the problem with presenting royal flush separately: you have to deal with people who think that something comes between royal flush and straight flush. This may well be a much rarer problem than the "where is the 'royal' flush?" alternative, but I think it's a more insidious problem because the "where is the 'royal' flush?" person knows they are confused so they ask and it is quickly fixable, while my "4 of a kind beats straight flush" person may not know until the worst possible moment: a game where the difference matters.

@BenjaminCosman New players have confusion as to the order of hands quite frequently.  Many new players I've played with cannot remember the relative ordering of a straight, a flush, and a full house (and have seen a few hands go horribly wrong for players who were confused about this).  This is why an order of hands reference is important.  I agree that including a royal flush in a hand ordering adds unnecessary complexity.   When I'm teaching the game, I use hand order references that don't have a royal flush as a separate category (ex. https://boardgames.stackexchange.com/a/53389/9999).

I would think this has something to do with the fact that a straight flush has multiple card combinations per suit to achieve it, making it more common (2, 3, 4, 5, 6/ 8, 9, 10, J, Q etc...) and the Royal Flush only has one card combination per suit (A, K, Q, J, 10).
The Royal Flush could be a straight flush also in theory, (I understand this is where your confusion lies) but the fact it has all of the Royalty cards in it, makes it a one of a kind "straight flush" in the suit. It also stands to reason that it is a lot more valuable of a hand than a normal straight flush as it has all of the highest value cards in it.
The only real supporting evidence for the origin of the name Royal Flush is literally only in the dictionary. It states that a Royal Flush is made up of the top 5 "honors" of any suit. To me the word Honor further suggests Royalty. The fact that Royal figures (King and Queen) are in the line up of a Royal Flush is the best suggested evidence of its origin.


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Is Pandemic Legacy as good with 3 players as it is with 4?
I have gathered 3 players (including myself) for Pandemic Legacy and we are eager to begin, but I'm wondering whether I should take the time to find a 4th. I've played Risk Legacy with 4 and it was a great experience. I'm somewhat concerned that the 3-player version of Pandemic Legacy won't be as deep or engaging as the 4-player version. This is just speculation, however, I have no evidence to back this up. Hence this question. Thanks!

As far as I know, the game was designed to be balanced at 2-4 players just like normal Pandemic. Outside of that, I'm not sure you can get an answer that isn't just someone's opinion.

The answer to this will depend on your group

This is an opinion-based question and does not fit the Q&A format for this site. Try BGG they keep track of # of player recommendations.

@freekvd - subjective questions are not banned here.  Please consult our FAQ I don't believe this question crosses any boundaries.

@PatLudwig I have rechecked the definition for "primarily opinion-based". If this question doesn't fit it, then I don't know which does.

@tsuma534 - In my opinion, the questioner is asking for folks to share their experience and expertise with the game.  Check the answers below, did they use facts, references, or specific expertise to support their opinions?

We've played the game with both 3 and 4 in the same campaign.  It didn't affect the feel of the game either way.  For a variety of reasons you likely won't play the same characters in every mission anyway, so there is no reason that you can't add or drop someone part way through.

There is even a space in the occupation cards' play logs to note who played them that session.

Now that I've played the game with 3 players (we're at the end of october right now) my feeling is a little more contrasted:

the game works perfectly well in this configuration (and is a blast BTW)
you might get more variation in the characters played by adding a fourth player

Our experience was that with 3 players, we almost (at least at the beginning of the campaign) always played the same subset of characters. You don't always get to play the same role as you attribute them at the end of the setup, depending on the cards in hands and the situation on the board but still. We were often arguing:

hey we could get use of this one this time!
Yeah sure, which one of the fab 3 do we remove?
OK let's keep'em

I'm on the same boat...
We decided that it was better for us to start playing with 3 players than to wait for a fourth one that can be as available and motivated as the 3 of us (and possibly never play at all)...
We didn't start playing yet, but here are the way we envision it:

The fourth spot might become available for a friend of us who would want to try the game but can't commit to the full campaign (think of it like guest-stars in the Muppet Show back in the day)
if we feel like the game is less fun without the 4th pawn/character, as everything is open information (that's my understanding from reading the rules), we can still add it and decide collectively for its actions...

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sort: votes


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Good Risk strategy suggestion?
I'm looking for good Risk strategy suggestions. I tried a couple of things like conquering smaller and easier continents, going for territories which I have a card for but none of this yielded awesome results.
Any help from a guru?
Thanks

Voting to reopen. Risk is a well-established game, there are only a few good answers to this question. I don't see this close reason being relevant at all.

@freekvd thing is, i get similar answer wherever i ask so i kinda gave up in the question..

Pertinent meta: Should we close question that are just "what are good strategy tips for such-and-such game"?

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text:
What are the rules of this "Frog rescue game" from Boots?
I picked up this game second hand but found it doesn't include any instructions.
It has a cross-shaped board that you assemble jigsaw style with a tower in the middle. The back of the box says "in the exciting race to the castle, all the dice are rolled together on each turn and all the players move at the same time". Dice are coloured, one matching each player. But there also appear to be some elaborations on the basic structure of rolling dice and advancing eg there are some special squares - dragons and thorny bushes - and each player has three different characters - a knight, a wizard and a princess.
We'd love to know how all this is implemented. Of course we can make up our own house rules but would like to know the official ones too.
There's a date on the inside of the box of 2004 which could be when it was manufactured.
[1]:

Who is the manufacturer? Do you have a pic of the front of the box? Is there a copyright date shown on the box or the board pieces?

@L.ScottJohnson Picture added of the other side. No date that I can see. Manufacturer is Boots, a large UK pharmacy.

The box has a 'Boots' logo.  For those outside United Kingdom that's a high street store that sells mainly health care products.  The branch where I live a a baby/children's section where such a game could be found.  If this game is in print or not I've no idea as I can't find this game listed anywhere.  It might be worth contacting Boots directly to see if they can help you.

Actually, just spotted a date on an inside flap of 2004.

Have you searched online using the barcode?

@bensvenssohn thanks for the suggestion! No luck though, unless there are any special tricks. I just googled barcode 5045094703395

I suspect that if you were able to get the website archived at http://web.archive.org/web/20050307215227/http://www.bootslearningstore.com/stuck.htm to load (It requires Flash 5), you might find the rules or at least more hints at them, but that's where I got stuck.

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Stack resolving with planeswalker and instants
I play Nissa, Voice of Zendikar a planeswalker. When it's in play my opponent plays Devour in Flames to deal 5 damage to my planeswalker. I want to use my effect "put a +1/+1 counter on each creature you control" what will be resolve first? Does my creatures get +1/+1?

If you want to talk about instants instead of sorceries, are you OK with replacing Devour in Flames with Fated Conflagration? This Nissa enters with 3 loyalty counters. Does it matter that the spell does 5 damage? Does that mean that her +1 loyalty ability has been activated already? Or do you mean that this is happening right after she enters the battlefield?

Yeah its more the if its an instant what would happen, can nissa take damage at the moment of summoning or just after. Could she get damage before shes on the battlefield

Nissa, Voice of Zendikar is a Planeswalker, which means that you can only activate her abilities on your turn, and Devour in Flames is a Sorcery, which means your opponent can only cast it on their turn. In other words, if your opponent is able to cast Devour in Flames, then you don't have a chance to activate Nissa's ability.

But if it were some instant card or ability that did the damage, after the planeswalker resolves the stack is empty and the active player has priority, so you can always choose to activate a planeswalker ability immediately after it resolves.

Sure, with different cards, played at a different time, you would have a different interaction.

The following assumes that Devour in Flames can be cast by your opponent at instant speed.
Unless Nissa, Voice of Zendikar entering triggers a triggered ability creating a stack, you will immediatly receive priority and be able to activate the loyalty ability before your opponent can cast Devour in Flames.
If Nissa, Voice of Zendikar entering triggers a triggered ability, then stack will not be empty and when you pass priority, your opponent can cast Devour in Flames to destroy Nissa before you can activate the loyalty ability.
From the Comprehensive Rules:

116.3. Which player has priority is determined by the following rules:
116.3a The active player receives priority at the beginning of most steps and phases, after any turn- based actions (such as drawing a card during the draw step; see rule 703) have been dealt with and abilities that trigger at the beginning of that phase or step have been put on the stack. No player receives priority during the untap step. Players usually don’t get priority during the cleanup step (see rule 514.3).
116.3b The active player receives priority after a spell or ability (other than a mana ability) resolves.
116.3c If a player has priority when he or she casts a spell, activates an ability, or takes a special action, that player receives priority afterward.
116.3d If a player has priority and chooses not to take any actions, that player passes. If any mana is in that player’s mana pool, he or she announces what mana is there. Then the next player in turn order receives priority.

and

606.3. A player may activate a loyalty ability of a permanent he or she controls any time he or she has priority and the stack is empty during a main phase of his or her turn, but only if no player has previously activated a loyalty ability of that permanent that turn.

EDIT: A spell can't be cast until the player has priority. The trick is that the active player (whoever's turn it is) receives priority immediately after Nissa enters the battlefield.
If there is no stack, then the the active player may choose to activate one of Nissa's loyalty abilities. In response the opponent can cast Devour in Flames (assuming it is instant speed), but the loyalty ability will already be on the stack. What will happen is: Devour in Flames will resolve and Nissa will be destroyed and then Nissa's loyalty ability will be resolved.
If there is a stack (for whatever reason) then the active player cannot and after passing the opponent can cast Devour in Flames (assuming it is instant speed). Devour will resolve, destroy Nissa and the active player has no chance to activate the loyalty ability of Nissa.
Also you cannot cast a spell that targets a planes walker while the planes walker is being cast, since at that time the planes walker is a spell and not a permanent.

But if devour of flames was an instant. Could such an instant be played when the planeswalker is summoned? Or after the summoning?

I editing my answer with more explanation.

So if i activated the ability first i will get the benefits of nissa her ability's and if the instant is first i wont get the benefits of nissa's ability.

You are correct.


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Trading Property to settle a debt in Monopoly
Player 1 has landed on Player 2's property and cannot afford the rent. Can Player 2 accept a property with money to settle the debt?
Example: Player 1 owes the rent of 500, they have 400 and a property worth 100 (according to the bank). Can Player 2 accept the money and the property to settle that debt?
This could be considered a trade and it the official rules don't explicitly restrict the time at which a trade can be completed. (However, since it could be considered a trade, Player 2 could consider the property to be worth what they want [and therefore worthless] to bankrupt the Player 1)
As a family, we have always played it so that the property is worth the equivalent of its face value. We chose this because it reflects the "real world" in a more accurate way.
However, after re-reading the rules, taking them at very face value, you should be bankrupt the moment that you cannot afford the rent after mortgaging and selling houses (if by doing that it will cover the rent).
I'm now more on the side of bankrupting without allowing for trading. However, we've been keeping high scores since 2002, it might not be worth it.
Summary:
When a player cannot pay rent with money, mortgages and buildings, the rules can be interpreted in 4 ways:

the player is bankrupt immediately.
the player may trade with the other players, except the creditor.
the player may trade with any other player.
the player may use the face value of the card to pay towards the debt.

The fourth option is neither in the rules nor a reflection of the real world (if you are known to be desperate for cash, you can't expect to receive normal price for what you sell). Is your house rule that the creditor can accept the normal value (in which case it is the same as option 3) or that he must?

@Gendolkari I would argue that it is not a duplicate as it extends the trading to the debtor also.

@TimLymington You're right about that. I think in general it is that we must accept it at face value which is not part of the rules.

@Thomas'Panda'Attwood I could be wrong, but the way I read it, both questions are really asking "can a player who cannot afford to pay his debts still trade with people to get the money to pay them, or does he immediately lose?"

And every answer given on that other question answers this question just as well.

I think it's pretty clear that this is a duplicate. If you can trade with a third party, you definitely can trade with your debtor. The idea that you might not be able to trade with your debtor but could trade with someone OTHER than your debtor is a very weak argument.

I still disagree, especially because that was specific with third party whereas this is specific with debtor. It would have been difficult to add this to those questions/answers at this point, which was what I was thinking about doing.

What's unclear about the rules:

You are declared bankrupt if you owe more than you
  can pay either to another player or to the Bank. ....
... A bankrupt player must immediately retire from the
  game. The last player left in the game wins.

Unless one can find a way to clear the entire debt while retaining an asset of at least $1 value, thus avoiding bankruptcy, the bankrupt player is out of the game; just as the rule stipulates.
Part of the beauty of the game is the simplicity of the rules as written. Imagining considerations that are not actually in the rules is what leads to games dragging on for hours; I for one would rather concede a lost game and get started on a second.

What's unclear is if "you owe more money than you can pay" includes the right to make trades in order to raise the money to pay. In other words "can pay" is unclear. "I can pay IF someone agrees to buy this property." See the linked duplicate for more discussion.

An asset of $1? Or simple no debts. You aren't bankrupt if you have $0 but also owe $0.

After re-reading the rules, I now agree with what you're saying, especially as it reduces the time of the games (although, we have never had an issue with that). However, the rules don't make that explicit enough, as Gendolkari explains.

@corsiKlauseHoHoHo: Yes, I have corrected the wording to properly represent that. Not quite sure why I thought the more verbose wording was better.

Unfortunately the rules are far from clear about exactly what you can do in your attempt to avoid bankruptcy. You can sell houses and mortgage properties (because that is mentioned); thereafter there is a slippery slope of selling properties, selling other assets (perhaps agreeing not to demand rent next time round), and making various deals with the creditor.  None of these are explicitly allowed or forbidden; which are permited presumably depends in house rules.

@TimLymington: From the 204 Official Monopoly World Championship Tournament Rules (http://funskool.indiatimes.com/rules.html): All trades are based on assets owned at the time of trade. No options or immunity from paying future rents may be granted, nor may partnerships be formed. and Trading is permitted during a player's turn or in between other players' turns, but not during an opposing players' turn.. Therefore no 3rd-party trades, as that would be during another player's turn (if they avoid bankruptcy) or subsequent to their departure from the game (if they don't).

@TimLymington: Althougf worded differently, the Official Monopoly Tourney Rules (http://monopolytourney.com/rules-html/) have the same effect: There are no side deals when a person is going bankrupt.  The person may only be in transaction with the player who is bankrupting them.


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Dead of Winter - Too easy with no betrayer/co-op?
Co-op variant (hardcore) or games where the betrayer is obviously absent seems easy after playing the game a couple of times. Even with the betrayer, we find we can keep the morale 7+ consistently.
We usually start off getting weapons from the police station then arming the the few colony guys (e.g janitor/bev), while sending the rest to search at locations depending on objective/crisis, leaving them there and using the colony guys to attract the zombies back and kill them; playing outsiders sparingly.
The problem is we are never really moving after the initial first/second rounds, and we rarely need too much food (unless playing the food objective). And the guys in the colony get armed with like double sniper switchblades as we keep searching the police station without penalty.
Are we doing anything wrong?

Yes, Dead of Winter without a betrayer (especially without hardcore objectives) is easy, even extremely easy with 4 or 5 players. Even so, hardcore versions of objectives can be difficult if you play them with 3 players (and some are impossible with 2 players, literally impossible).
While it might not be the case for your group, I'd argue that Dead of Winter can be very easy if there is no betrayer but there is an alpha player. Without a betrayer the alpha player can easily convince the group what to do and essentially win the game solo. This is a problem that most co-ops have, and this is exactly why I always play with the betrayer.
You also might want to reread the rules, or at least watch a "Watch it played" video to make sure you aren't skipping any vital rules by mistake.

tl;dr Dead of Winter scales poorly.

We missed the rule that you can't move a survivor more than once for a long time. That makes the game a lot harder. I'm not sure any of the hardcore missions are impossible on hardcore. Although Home sweet home is extremely difficult on 2. You basically need luck to achieve it.


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Is it OK to mix Colony Wars and Frontiers for a 2 player game?
Is it OK to mix Colony Wars and Frontiers for a 2 player game? Would there be any balance issues?
One main worry is that the trade row might just have high value cards for a while and you are just sitting there buying explorers for a long time

"Balance" typically refers to each player's relative chances of winning.  There isn't any inerrant balance changes from the expansions because the trade row is shared between the two players.  Even if the trade-row gets full of high-value cards, the game does not favor one player over the other.  Unaffordable trade rows happen even with just the base game (I've seen it happen), and Explorers exist for this very reason.
Balance issues aside, all of the Star Realms expansions have a spread of card costs.  I do not believe any of them significantly increase the chance of an un-affordable starting trade row.

If you are worried about the trade row being too expensive, by far the most important factor will be the average cost of the cards in the deck. From the card gallery, you can calculate that the average costs in the three large sets are
Core Set: 3.6
Colony Wars: 3.525
Frontiers: 3.4
Thus both the expansions have less expensive cards than Core Set; mixing them together will still result in a less expensive deck.
Technically having a bigger deck does increase the variance of costs you may see. As an extreme example, if you played with a 5 card deck of costs 1,2,3,4,5, then you would always see all 5 costs on the trade row at the start of the game, whereas if you played with lots of copies of that same deck shuffled together, then you would occasionally see starting trade rows of all 1s or all 5s, even though the average value hasn't changed. However, while I haven't crunched the numbers, my guess is that at the scales we are talking about (80-card sets), this effect is not significant compared to the averages discussed above.
There are other things you could also analyze, like

The variance within each set. For example a set with only 2s and 8s in a 2:1 ratio and a set containing only 4s each have an average cost of 4, but would play rather differently.
How much Trade is produced by the average card in the set, especially the cheap ones (since these can be bought early and then help you buy everything else).

Applying these to the real game is left as an exercise for the reader.

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Clank! Legacy Necrosis Rules
! Clank! Legacy Spoilers Ahead !
With Necrosis you need to Heal to get rid of the card.
If you have no damage can you Heal the  Necrosis with a forest space? Can you trash Necrosis at a volcano?

Having only played the base and in Space, my first thought based solely on your post is that you shouldn't be penalized for not having been damaged. If something would heal you if you had damage, it should heal the Necrosis even if you have no damage. Again, I haven't read the rules or anything of the kind.

My group's understanding of the rules was you need damage in order to heal. The text on the card states "If you ❤ this turn" meaning it is the result of an action. If there was no damage then there was no ❤ action taken.

Are there any official rulings to back up your opinion? Necrosis seems like an aliment that would need a cure, such as forcing to stop at a healing location or spend a healing token to get rid of it.

In the "Step 4: The Getaway" section of the base game it specifically states that healing happens damage is taken.  This and the rest of the text can all not be accomplished if there is no damage cube. Obviously, if you want to make a house rule to make the necrosis less punishing that is totally up to your party! Games are for fun.

correction, the exact words are "Some effects can heal damage you've taken".


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Could A Taoist Split Movement?
One of the Red Taoists abilities allows him to move twice. Could that taoist possibly split their movement?

Move Once (1)
Exorcise or Use Village Tile
Move Again (2)

Similarly, can any taoist pick the order in which they do their actions? For example, can a taoist attack first and move second or does the optional move have to be taken first?

Move always happens before your action. The red power doesn't affect this; it only makes the move part more powerful.
From the rules:

After the Yin phase is done, the player plays the role of his Taoist, according to the
  following sequence:
1) Move (optional)
2) Request help from a villager OR attempt an exorcism


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Do you use the Djinn you attain from the Sibittis ability' immediately?
The Djinn Sibittis has an ability which states:

Draw the top 3 Djinns from the top of the Djinns pile; keep 1, discard the 2 others.

In the rules under Sacred Places it has a point which states:

You can use the special powers of any Djinn you took right away, without waiting; however if there is a cost, you must be able to pay that cost now.

Would a player possibly be able to trigger 2 Djinn abilities using Sibittis? The first being Sibittis, the second being the Djinn you attain using Sibittis ability.

You can use the special power of a Djinn using Sibittis, yes, by the text you quote. If you mean can you use Sibittis's ability twice in one turn, then no.
This is also true without invoking Sibittis. If you have multiple Djinn cards, you can use each one once per turn.
Details from this thread on BGG.

Each djinn can be used once per turn in any order you want. If u dont want to use them all u dont have to. Just cant use the same one twice.

Q: If you buy Sibittis, you can use him straight away (that's fine). But, can you use the djinn you get from his ability immediately as well?
A: If it has an activation cost, yes. The rules make no distinction.

There is no limit on the number of djinns you can use in your turn, as long as you can pay the activation cost. Nothing in the rules suggests otherwise.

I guess your 2nd quote answers my question. So if the player attains a new Djinn using Sibittis ability, they're able to use the ability of the new Djinn as well. This means that a play may be able to use the ability of 2 different Djinn in one turn. I've updated the last line of my question for clarification purposes.

Right. This is true with or without Sibittis: you are always free to use each Djinn you have (once each).


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How to spend attribute symbol on Gear card?
We have this hacking rig gear card. Do we discard to use the mechanic attribute on the test? Do we just automatically get it if it's in our hand? Can we just keep stacking those cards to keep boosting our stats?
Cards include: Hacking Rig, Fancy Duds, Fake ID

Unless it says to discard, no, you may keep using it.
Yes, you automatically get it if you assign it to the crew on the mission. Each crew can only hold one equipment per mission (with some exceptions for specific crew and equipment). See the main instructions for more on the rules for equipment carrying limits and how mission assignment works.
Assuming you have multiple crew to carry each of the items you're using and they're all involved in the mission at this point, yes, they skill icons stack for skill tests.

Thanks, this makes more sense - for some reason we weren't viewing it as a traditional gear card that needed to be equipped to be useful. We thought it stayed on your ship until it was needed to be used.

@Howdy_McGee LORE: Someone has to hold the hacking rig and press the buttons on it.  ;-)
But yes, pretty much everything you purchase that isn't hiring crew, is gear.

@Mufasa Or ship upgrades, which attach to your ship upgrade or engine slots.


text:
Mercurial Pretender and Typhoid Rats interaction
Player A has Mercurial Pretender on the board (copied a 4/4 creature)
Player B attacks with Typhoid Rats
Player A blocks Typhoid Rats with Mercurial Pretender
Player A then pays 4 mana to "Return this creature to his owner's hand"
Player A returns Mercurial Pretender to his hand, then says Typhoid Rats dies and goes to graveyard.
Player B thinks that player A cannot both successfully block and return Mercurial Pretender to his hand, considering Typhoid Rats Deathtouch ability.
Who is right?

The specifics of player B's claim don't match up between the question and 2 of the below answers (though they are very informative otherwise). I'm not sure how to resolve this since editing would change the intent of either the question or answer.

As noted by Hackworth, Player B is correct under the current rules that the Pretender can't kill the Rats if it is returned to hand. However, it did still block them successfully and the rats won't deal combat damage to Player A or anything else this combat.
One possible source of confusion in the situation is that it used to work the way Player A thinks. You could "put damage on the stack" then play abilities in the combat damage step in response, before the damage resolved.
This was removed with the 2010 major rules update (the one that also changed Lifelink and Deathtouch). Now, player B is correct, because there is no place to respond between assigning and resolving damage.

Damage didn't origonally use the stack, it was added IIRC in 6th edition, then taken out later.

While it didn't "use the stack" in the same sense as it did in 6th edition, you still assigned damage, then had an opportunity to play spells; it may have only been damage prevention, regeneration, and interrupts, but there was definitely an opportunity to do something between damage assigned and damaged applied.

Player B is right.
In each combat damage step (First strike/double strike, then other creatures), all creatures deal their combat damage at the same time, and you don't get the chance to cast spells or activate abilities:

510.2. Second, all combat damage that’s been assigned is dealt simultaneously. This turn-based action doesn’t use the stack. No player has the chance to cast spells or activate abilities between the time combat damage is assigned and the time it’s dealt.

Importantly though, players can activate abilities between declare blockers and combat damage, so Mercurial Pretender can "successfully block" and then get returned to hand before any combat damage is dealt. In this case, Typhoid Rats does not die (because the blocker vanished before damage was dealt) but does not deal any damage to player A because even though the blocker is gone, Rats has still become a blocked creature.

Neither is correct.
Player A is wrong because he returned his blocker before combat damage was assigned and dealt therefore the attacker would not die.
Player B is wrong because player A can successfully block AND return his creature. The attacker's deathtouch ability is irrelevant.

This answer is correct. JKreft and Hackworth are technically wrong as they misinterpret what B said. They seem to have guessed at what the asker meant to say and then answered that.

If you ignore context and only look at Player B statement, sure. If you read it in-context, it is offered as a "Player A's statement is wrong" rebuttal. The rebuttal part "It doesn't work the way that Player A says it does" is correct, as our answers discuss.


text:
What is the actual world ranking of Fan Hui
I've read somewhere that Fan Hui was ranked between 600th and 700th world Baduk player. Knowing he's 2P whereas some players are up to 9P, it seems reasonable to me.
Is there any official and accessible world ranking ? What is the exact rank of Fan Hui ?

I believe your information comes from this unofficial rating system:
http://www.goratings.org/
Fan Hui's page on that site:
http://www.goratings.org/players/1480.html
Fan Hui only only played a few pro games - none recently - so his ranking there (or any other pro ranking system) is unreliable.
1P-9P rankings are not ratings (you only go up) and don't necessarily reflect the player's current strength.

Exactly what I was looking for. Also, the WHR algorithm used seems interesting.

Just to add a few notes in addition to Pieter's answer, and with a hint to your implied question (can AlphaGo beat Lee Sedol?):
First off, I'm not sure if you thought being 9p automatically means being stronger than 2p. This is not the case.
However, in this particular instance, other matters are of more importance. Fan Hui has not been competing in Asian (i.e. highest level) tournaments for many years, and his competition in Europe is limited - that's why he's the current European champion, after all.
However, this also means that it can be assumed that he's not quite as sharp as an active, competing pro in Asia. His focus simply shifted towards teaching, as teaching was the reason he came to Europe. That is to say, and with no disrespect to Fan Hui's great skill, Lee Sedol, an active top level competitive pro, is quite a bit stronger than Fan Hui - 2 stones, goes the rumor among pros.
Obviously, the closer we get to perfect moves, the more difficult it becomes to improve further: For instance, doubling AlphaGo's calculation power does not at all lead to doubled strength. Think of it more like a logarithmic scale: To improve another stone in strength, you have to put in just as much work as you did for all previous stones together (roughly speaking). It remains to be seen if AlphaGo's improvements since the Fan Hui games are large enough.
About comparing pro Go players
While we cannot compare pros by their rank, we can get a rough idea of their relative strength by using Dr. Taeil Bai's chart, of which I reproduce the beginning of the most recent version I could find (from cyberoro, 2014):

I am not aware if Fan Hui is included in the list, too - if he was, that might be the source for your 600th-700th information.

Interesting - thanks.  Do you have a URL for those cyberoro results?  How does the rating system used at WBaduk compare, which seems to only be applied to amateurs (i.e. explained at http://www.wbaduk.com/wbaduk/rating_system.asp with actual ratings at http://www.wbaduk.com/wbaduk/wbaduk_ranking.asp (nasty use of html frames there - sigh).

The cyberoro image is from http://open.cyberoro.com/photo/201407/%5B519386%5D140722-pj-04.jpg, but I don't remember the corresponding articles. I don't know anything about the WBaduk schema, sadly.

Is there any official and accessible world ranking ?

No; Rankings are done by national Go organizations, with some variance existing between them.

What is the exact rank of Fan Hui ?

As reported here,

Fan [Hui] earned a 2-dan professional ranking in China before emigrating to France, so it appears that go software has reached the level of professional play.

and

..., but it is worth noting that the AlphaGo programming team reports that AlphaGo can beat the best rival computer programs with a four-stone handicap. That is something that several other 9-dan pros have had trouble doing in the past few years.

Thanks for the answer. I didn't AlphaGo had beat CrazyStones with 4 stones ! Interesting to note that Rémi Coulon (who made CrazyStone) has also created the rakings in the accepted answer !

Great links - thanks!  But since they tend to die over time, it is much more helpful to summarize the data more here.

@nealmcb I think he did a great job of providing useful links while only extracting the part that was directly relevant to the OP's question

Good point, @Christophe.  I think I was so caught up in the minutiae of the differences among the rating schemes that I forgot that the question here was pretty limited, and indeed more details wouldn't help a lot.  Though I think it would help to identify the sources more clearly and conveniently.  E.g. the "reported here" text refers to an article "Deep Learning Takes Computer Go to the Professional Level" by "ivan" on the International Go Federation site.


text:
How do I chose invasion or reduction points?
I have the following board:
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . a . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . b . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . . . . . . . . X X . O . . . . . |
$$ | . . . . . . . . . . . . X . . . c . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

Now, white territory is rather large. So I like to decrease it!
However, I have the following problems/questions/considerations:

I will lose every KO battles elsewhere on the board (I have around 70 points hanging that I will win, but my opponent can play 5-10 stones that I must react at.)
I can invade both a, b and c. Does invading at a make b impossible? Is b even possible? Is c even possible?
How many points should I estimate for a invasion at a, b and/or c?
Should I start this invasion as soon as possible or delay it?

Maybe we should shape this question more towards "How do I chose invasion or reduction points?", as that would be easier to search for by others and also reflect the core problem better.

@mafu: Done. I will accept your answer once i had time to fully study it. It's kinda long you know :-)

First off, count the current score. If you're winning, do not invade. Just make sure you keep white small enough that you still win.
Let use further presume that black would be losing. You counted, so you know by how many points. A move around c could be parried with a sacrifice of two white stones while sealing off the rest of the upper right corner completely. So, if you're only behind a bit, you should probably play around c.
If you need to invade deeply, you probably made a mistake earlier - why do you need to invade that late, after leaving such a large area for the opponent? Try to find a better invasion or reduction time when you review the game, and look out for similar situations in the future. Good invasion and reduction timing is very important, and you'll soon learn to avoid trouble like this beforehand.
But maybe you could not prevent it (or made a honest mistake), and arrive at the current board, far behind. You need to invade deeply. You also already identified a few usual spots at a and b, but there are many more to consider.
When invading against that many opponent stones, you cannot expect a good result. Considering it's roughly 10 vs 1, even living small in ko should be considered a success. That black always ends in gote is understood. I'm aware that, especially for weaker players, it may sometimes seems more like a gamble, but don't worry about that. We'll try to find a few useful ideas how to deal with this. This is actually a very, very broad topic and I'll try to stick to the most important things.
In advance, I apologize to the reader if the following is too short an explanation. I'm writing this mainly for players in the 4 kyu to 12 kyu range, as that's where these problems typically become most prevalent, though weaker players may hopefully be able to profit from it, too.
Direct invasion at 3-3
If black invades at a, I would definitely want to kill it as white:
$$cm1
$$ -----------------------+
$$  . . . . . . . . . . . |
$$  O . . . . . 8 6 . 5 . |
$$  O . X . . O . 7 1 . . |
$$  . X . . . . . O 2 3 . |
$$  O O O . . . . . . 4 . |
$$  X X O O . O . . . . . |
$$  . . X . . . . . . . . |
$$  . . . . . . . O . . . |
$$  . . X X . O . . . . . |
$$  . . . . X . . . . . . |

A useful technique can also be black 4 in the following diagram, which kind-of-reverts to the above. You may want to remember this move, for if applied at the right time, it can throw off an unaware opponent completely.
$$cm1
$$ -----------------------+
$$  . . . . . . . . . . . |
$$  O . . . . . . . . . . |
$$  O . X . . O . 2 1 . . |
$$  . X . . . . . O 3 . . |
$$  O O O . . . . . 5 4 . |
$$  X X O O . O . . . 6 . |
$$  . . X . . . . . . . . |
$$  . . . . . . . O . . . |
$$  . . X X . O . . . . . |
$$  . . . . X . . . . . . |

You should consider other points for invasion, too. I'm sorry that I won't show many variations, for that would inflate this post too much. Please research them on your own - it will be worthwhile, as these will surely come up in your games sooner or later.
Attaching the corner
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O 1 . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . . . . . . . . X X . O . . . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

This is a variant that is usually played as a regular joseki, however, it is unlikely that a joseki would develop on this board - white has too many stones that allow her to deviate for a better result.
But it is not all moot yet. Its basic idea is: When you're weak, you want to touch the opponent and force him to either draw back strongly (white grants you additional stones in the area for almost free), or touch back (typically with a hane), which often leads to cuts in their shape that you can try to use to force an exchange. This is actually an extremely important idea to keep in mind in such situations.
Please research the (too) many possible variations on your own. Joseki books should give a good points which moves are important, but remember that white is free to deviate.
Submarine, straight below hoshi
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . a . . |
$$ | . . . , . . . . . X . . . . . O b 1 . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . c . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . . . . . . . . X X . O . . . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

This is a rather common joseki move, too, though again, everything is different on this board. White usually replies at a, b or c.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . 2 . . |
$$ | . . . , . . . . . X . . . . . O . 1 . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O 3 . . |
$$ | . . . . . . . . . . X X . O . . . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

If white protects the corner with 2, black would surely extend to somewhere around 3, and hope for living or connecting somehow.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . b . |
$$ | . . . , . . . . . X . . . . . O 2 1 . |
$$ | . . . . . . . . O O O . . . . . . a . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O d . . |
$$ | . . . . . . . . . . X X . O . . . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

If white bumps down at 2, black can decide between a and b, which are probably miai. If black a and white b, black would again play at or around d next.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . b . . |
$$ | . . . , . . . . . X . . . . . O . 1 . |
$$ | . . . . . . . . O O O . . . . . a . . |
$$ | . . . . . . . . X X O O . O . . . 2 . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . . . . . . . . X X . O . . . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

One of the strongest moves is this white 2. Note that if black a, white b, and black has extremely poor eye shape, which is not acceptable on this board. So black must play at b next, and the corner becomes a tsumego, of which I don't know the resu..--- eh, I mean, which I assign to you as homework.
Submarine, low keima from the hoshi
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O a b . |
$$ | . . . . . . . . O O O . . . . . c 1 . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . . . . . . . . X X . O . . . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

This is another usual point, and white can reply at a, b, c, or possible elsewhere.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O 2 . . |
$$ | . . . . . . . . O O O . . . . . . 1 . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O 3 . . |
$$ | . . . . . . . . . . X X . O . . . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

Nobi defense at 2 would revert to a similar situation as before, and black would look forward to play at or around 3 next. Life is not guaranteed here, though. It seems the 1-2 exchange benefits white more than black, because it removes a lot of options in and nearby the corner.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O 3 2 . |
$$ | . . . . . . . . O O O . . . . . a 1 . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . . . . . . . . X X . O . . . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

Tsuke tobi at 2 is unlikely on this board as it seems to give black too much wiggle room: Refer to the joseki after the moves 1-2-3-a.
$$cm1
$$ -----------------------+
$$  . . . . . . . . . . . |
$$  O . . . . . . . . . . |
$$  O . X . . O . . 4 6 . |
$$  . X . . . . . O 3 2 . |
$$  O O O . . . . . 5 1 . |
$$  X X O O . O . . . . . |
$$  . . X . . . . . . . . |
$$  . . . . . . . O 7 . . |
$$  . . X X . O . . . . . |
$$  . . . . X . . . . . . |

White would never play atari from the inside at 4, as then black could play 5 in sente and extend to 6, which is too good for him.
Low keima approch
You suggested a regular low approach. White would probably defend the corner solidly, or kick.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O a b . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . 1 . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O c . . |
$$ | . . . . . . . . . . X X . O . f d e . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

If white defends the corner at a or b, black would probably move back to play c and hope for a double hane (c-d-e) (or possibly crosscut with c-d-f) and good exchange. As a and c are miai, if white blocks at c, black would play at a (or possibly 3-3) next, and hope to live locally.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . 2 . . |
$$ | . . . . . . . . X X O O . O . 3 1 . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O 4 . . |
$$ | . . . . . . . . . . X X . O . . . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

If white kicks, black cannot afford the usual move at 3, because white would immediately come back and play 4, after which black is heavy. Note that the 3-3 offers a lot of aji, but here white is so strong that even that won't suffice.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . 4 . |
$$ | . . . . . . . . O O O . . . . . 2 3 . |
$$ | . . . . . . . . X X O O . O . a 1 . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O 5 . . |
$$ | . . . . . . . . . . X X . O . . . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

Black would instead hane at 3, after which white would surely play 4 (alternatively, white a may be interesting and not expected by any opponent). Black would then attach back at 5, and it would not be easy for white to capture the whole group.
Various exchange offers
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . . . . . . . . X X . O . a b . . |
$$ | . . . . . . . . . . . . X . . c d . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

The moves around a to d give white the option to seal off the corner, while black captures 2 white stones. If this is acceptable for either player, and which of the moves is best, requires just a lot of normal, boring reading and counting.
Hybrid approach
If you remember the attachment idea from above, you may think about this move:
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . a c . . |
$$ | . . . . . . . . . . . . . . . O 1 . . |
$$ | . . . . . . . . . . X X . O . b d . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

If white draws back solidly (at a or b), black got an almost free stone, which will help him live locally. This is too soft in this case, so white would surely hane at c or d.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . 2 4 . |
$$ | . . . . . . . . . . . . . . 6 O 1 . . |
$$ | . . . . . . . . . . X X . O . 5 3 . . |
$$ | . . . . . . . . . . . . X . 7 . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

A very, very simple sequence could be black drawing back, then white just protecting the corner. Note that this would be better than black 3, white 1, which we considered earlier.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . 2 5 . |
$$ | . . . . . . . . . . . . . . . O 1 . . |
$$ | . . . . . . . . . . X X . O . 4 3 . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

If white pushes above at 4, black will definitely hane at 5 and try to live locally. This is dangerous for white, as she risks a lot more points if black lives (and he likely will, as white must spend another stone below 4 to connect her two stones and prevent black from moving in that outwards direction.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . 2 . . |
$$ | . . . . . . . . . . . . . . . O 1 . . |
$$ | . . . . . . . . . . X X . O . 3 . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

Black may also entertain the idea of counter hane, which may reasonable, as he's not much weaker than white on the right side - the two white stones are weak! The counter hane is a bit complicated, and will lead to an exchange, the quality of which depends on the players' fighting abilities.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . b . . |
$$ | . . . . . . . . . . . . . . . O 1 . . |
$$ | . . . . . . . . . . X X . O . a 2 c . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

If white outside-hanes at 2, black can think about a, b or c, which again depend on the players' fighting abilities. Black has several thinkable continuations here, because white's two stones are not strong.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . c . . |
$$ | . . . . . . . . . . . . . . . O 1 . . |
$$ | . . . . . . . . . . X X . O . 3 2 . . |
$$ | . . . . . . . . . . . . X . . b a . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

If black crosscuts, white's primary options seem to be drawing back at a, which increases liberties and also enables black 1 to be caught with c, so black is under some pressure.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . d O 1 . . |
$$ | . . . . . . . . . . X X . O b 3 2 a . |
$$ | . . . . . . . . . . . . X . c 4 e . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

If white ataris at 4, black would not counter hane at a, because if he wanted to do that, he should play a directly instead of 3. So black will move out at b, and white can continue with c, d or e, depending on her reading of the variations. White is in control of the direction more than black.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . a 3 . . |
$$ | . . . . . . . . . . . . . . . O 1 . . |
$$ | . . . . . . . . . . X X . O . c 2 b . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

If black pulls back at 3, the obvious replies are a, b or c. White a would be followed by black b, which seems to let b live or connect out eventually.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . 8 . |
$$ | . . . . . . . O O . X . . O . . 6 7 . |
$$ | . . . , . . . . . X . . . . . O d 5 . |
$$ | . . . . . . . . O O O . . . . 9 . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . e 3 . . |
$$ | . . . . . . . . . . . . . . . O 1 . . |
$$ | . . . . . . . . . . X X . O . a 2 4 . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

In response to white 4 or a, black would probably slide towards the corner at 5, and push for eye space with the sequence to 9. Considering d (and likely e, too) is sente, black may live there - if he believes he would not, he should chose different moves earlier.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . b . . |
$$ | . . . . . . . . . . . . . . . O 1 . . |
$$ | . . . . . . . . . . X X . O . a 2 3 . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

The counter hane at 3 would likely be followed by white a or b.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . . c . |
$$ | . . . . . . . . . . . . . . . O 1 . . |
$$ | . . . . . . . . . . X X . O . 4 2 3 . |
$$ | . . . . . . . . . . . . X . . . d 5 . |
$$ | . . . . . . . . . . . . . X . a . . . |
$$ | . . . . . . . . . . . . . X . O O b . |
$$ | . . . . . . . . . . . . . X X X X . . |

Magari at 4 invites black 5, which connects out or likely captures the two white stones with a, if white resists with the descend at b. Black can also consider playing c instead of 5 first, after which white would atari, black connect, white extend, and finally black d to connect out.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . 4 . . |
$$ | . . . . . . . . . . . . . . . O 1 5 . |
$$ | . . . . . . . . . . X X . O . a 2 3 . |
$$ | . . . . . . . . . . . . X . . . 6 . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

White 4 is a strong reply to 3, and up to 6, black is in danger. Black would look for an exchange, using aji such as the cut at a.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . 4 5 . |
$$ | . . . , . . . . . X . . . . . O 3 . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . 1 . . |
$$ | . . . . . . . . . . X . . . . 2 O a . |
$$ | . . . . . . . . . . . . . . . O X X . |
$$ | . . . . . . . . . . X X . O . . O X . |
$$ | . . . . . . . . . . . . X . . . O . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

For instance, if white replies to black's clamp at 1 with 2, black would play tsuke at 3 (instead of just a) to increase his options, and white becomes quite busy. Black should be able to live somewhere.
Note that black should not just play 1 at a, for white would then play 1 and black would be short of eye space.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . 1 . . |
$$ | . . . . . . . . . . X . . . . 5 O 2 . |
$$ | . . . . . . . . . . . . . . . O X X . |
$$ | . . . . . . . . . . X X . O . . O X . |
$$ | . . . . . . . . . . . . X . . . O 3 . |
$$ | . . . . . . . . . . . . . X . . . 4 . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

If white just cuts down at 2, black would white cut at 5, possibly exchanging 3 to 4 first. Black is still looking for an exchange, and the several sente moves he gains while white is trying to live the 2 stones should be sufficient.

Oh dear, what have I done

+1 for the detailed, insightful answer. As for the last diagram, I think that white 2 is actually a strong move and black will have a hard time making a base (c in answer to black b, a in answer to black c, and maybe Q10 in answer to black a).

@Christophe Thank you. Good points, and upon reading the variations again, I agree white 2 is a strong move there even if it's a bit risky. I've edited the question to take that into account. (The diagram your comment referred to is the fifth of "Hybrid approach".)

Great! In diag 11, white has a strong but risky answer at S12, so your diag 12 looks better than my initial suggestion. In diag 14, black doesn't get much after white S14.

@Christophe I have no idea how exactly black would continue after S14, but to me it looks like he can find some compromise/exchange. Not sure. Requires a lot of reading obviously, which I wanted to avoid doing too much of in this post (I was trying to keep it somewhat generic so the ideas apply to different boards, too). Let's just hope S14 does not completely destroy black :)

Black might be able to save Q13 but that's about it... Let's just say that playing R12 directly doesn't look like the best option for black.

Great answer, almost too good as I think it won't find the attention it deserves here. Gave me a lot of insight into what might still be possible in a situation that looked completely uninvadable to me before! Also gives me some nervous fright when I imagine to be white and feel all settled and safe... (I'm around 10k at the moment).

$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . a . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . 1 . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . . . . . . . . X X . O . . c . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

b looks good as a probe, it makes miai of following up with either a or c. Note the symetry in white's shape.
Below a possible follow up. After black 7, a and b are miai. White needs to be careful as there's still a weakness at c.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O 2 . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . 1 . . |
$$ | . . . . . . . . . . X . . . c . . . . |
$$ | . . . . . . . . . . . . . . . O 4 b . |
$$ | . . . . . . . . . . X X . O . 6 3 . . |
$$ | . . . . . . . . . . . . X . a 7 . 5 . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

If white blocks on the other side, a san-san invasion becomes possible with the help of the R14 stone. Black gets a smaller territory than in the previous diagram, but still has options around R10 for later.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . 8 7 . |
$$ | . . . . . . . O O . X . . O . 6 3 9 . |
$$ | . . . , . . . . . X . . . . . O 4 5 . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . 1 . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O 2 . . |
$$ | . . . . . . . . . . X X . O . . . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

The attachment at R16 is usually a good stabilization move, but doesn't work so well here because of the surrounding white stones. The black shape is left without eyes even if Q16 gets captured.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . 8 . |
$$ | . . . . . . . O O . X . . O . . 4 5 . |
$$ | . . . , . . . . . X . . . . . O 3 6 . |
$$ | . . . . . . . . O O O . . . . . 7 . . |
$$ | . . . . . . . . X X O O . O . . 1 . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O 2 . . |
$$ | . . . . . . . . . . X X . O . . . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

Starting at the san-san is another interesting idea. White might kill the corner, as explained in mafu's answer, but the aji of the cut at a will force white to pull back after black 9. To avoid this, white can choose to let the corner live small. If white starts a ko, then black will have ko threats around Q11.
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . 8 6 . 5 . |
$$ | . . . . . . . O O . X . . O . 7 1 . . |
$$ | . . . , . . . . . X . . . . . O 2 3 . |
$$ | . . . . . . . . O O O . . . . . a 4 . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O 9 . . |
$$ | . . . . . . . . . . X X . O . . . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

Whether you start with R14 or R17, the key idea is to use that first stone as a probe and be ready to abandon it.

What insight does this provide that adds to the post by mafu?

@PieterGeerkens I believe c is a vital point here (better than attaching under Q12).

Nice spotting the 3+5 shape, it reduces quite a lot and has good yose properties. Also surprisingly safe.

I decided to revisit this post with the help of Leela Zero.
LZ's assessment is that there is no good move for black above the 11th line. The sequences are fascinating, here is the start of one:
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . 6 . |
$$ | . . . . . . . O O . X . . O . . 3 . . |
$$ | . . . , . . . . . X . . . . . O . 5 . |
$$ | . . . . . . . . O O O . . . . . . 4 . |
$$ | . . . . . . . . X X O O . O . . 1 . . |
$$ | . . . . . . . . . . X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O . 2 . |
$$ | . . . . . . . . . . X X . O . . . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O . . |
$$ | . . . . . . . . . . . . . X X X X . . |

Black's best move is at R11. The sequence would then depend on the value of the initiative, here is one that is similar to what I posted 3 years ago:
$$cm1
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . O . . . . . . . . . . |
$$ | . . . . . . . O O . X . . O . . . . . |
$$ | . . . , . . . . . X . . . . . O . . . |
$$ | . . . . . . . . O O O . . . . . . . . |
$$ | . . . . . . . . X X O O . O . . . . . |
$$ | . . . . . . . . . . X . . . . . . 8 . |
$$ | . . . . . . . . . . . . . . . O 2 7 . |
$$ | . . . . . . . . . . X X . O . 4 1 . . |
$$ | . . . . . . . . . . . . X . 6 5 . 3 . |
$$ | . . . . . . . . . . . . . X . . . . . |
$$ | . . . . . . . . . . . . . X . O O 9 . |
$$ | . . . . . . . . . . . . . X X X X . . |

Given the size of White's territory, you are probably behind. Then the question is, can you catch up, and if so, how? I'll save the first question for last, and answer the others in order:
2) You have the choice of ONE invasion point, a, b, or c (or some alternatives mentioned by other posters). Choosing one strengthens White sufficiently to preclude the others. Of three choices, b is "neither here nor there," and is least likely to work. If you want to invade around there, use the second-line "submarine" tactics suggested by others.
3) You can hope for a 10-15 point reduction by invading at c. That's not small, and is enough to decide an otherwise close game in your favor. An invasion at a) is potentially larger, 25-30 points, but it will be in ko, which is to say that you might net only the 10-15 that you would get "for sure" with c.
4) The decision should have been made earlier, but "better late than never." This is your "last clear chance" to win the game.
1) The ko that would result from an invasion at a is quite large. If your position is so shaky that you would lose every fight for a 25-30 point ko, you're probably lost anyway. If c doesn't work for you, your best hope is that you win the ko at a, by losing only 5-10 points to a ko threat, and winning 25-30 points as compensation.

Several points I don't agree with in this answer. First, as mentioned in other posts, the invasion at a is unlikely to result in a ko. Second, "neither here nor there" is typical of probes, and can be useful as support if not directly. Other than that, I find the general considerations very interesting.

Many question in one post ...
An invasion on a should work, because the corner is not yet 100% secure. White will probably build up strength to the outside leaving no potential on b. White will probably get the initiative afterwards.
An invasion on c looks very big, probably bigger than the corner invasion because of the two white stones to be captured. Maybe c is not the correct point to start the attack because a capping move by white (on the point left to c in the diagram) is a strong response, but the region is certainly interesting
An invasion on b is probably not feasible, but it can act as a question move which side white wants to defend.


text:
Are effects from attacks mandatory or optional?
Very new Pokémon tcg player (father trying to learn the rules here).
I wonder if the effects of an attack are mandatory or optional. Like I have a Alolan Sandslash whose Smash Turn attack  (requires 3 energies, deals 50 points) says to switch with a benched Pokémon afterward. This can be: very annoying if I am forced to switch with a base or otherwise weak Pokémon or it can be helpful if by switching I remove some condition or it can be impossible if I don't have benched Pokémon.
So, is it mandatory or optional? What if it is impossible to fulfil, can I attack nonetheless?

They are mandatory. With a simple comparison:

You can see that Alolan Sandslash's attack is mandatory, because it uses imperative tense, whereas Hitmonchan's first attack is not, because it uses "You may ..." phrase.
If you'd like a more reliable source, there is a list of official rulings named Pokémon TCG Rulings Compendium BW that contains many explanations how rules work with particular attack, card, or their combination. Here, you can find that there is a ruling for Bounce that we can use here:

Q. Can I use Emolga's "Bounce" attack if I have no bench?
A. Yes, you do as much of the attack as you can. First you do the damage, then you perform the switch if Emolga is able to go to the Bench. (Next Destinies FAQ; Feb 9, 2012 TPCi Rules Team)

This official ruling must be followed by all Pokémon that has the same attack (regardless its name), including your Alolan Sandslash. That means that you do the damage and then, unless you have no Pokémon on your Bench, you must switch it with with 1 of them.

Thanks. For me the step of finding a card with the same (or close enough) ability is not trivial since I am so new to the game (hence the very naive questions...)

"because it uses imperative tense" imperative mood /nitpick

Feel free to suggest an edit for that


text:
Pokémon attacks which deal no damage
I am learning to play pokemon tcg since my 7yo kid is interested into it and with his friends play a completely random version of the rules. At least I can try to give him some meaning and have fun in the meanwhile... My problem is that I can't find a reliable source of explanations like for MtG or keyforge and the rulebook is very incomplete.
One question that I have is how to use those basic Pokémon which have attacks which deal no damage. (e.g. Cosmog or Cosmoem). I assume that these aren't Abilities (which should be marked as such) and that I could use from the bench, but they are only attacks that I can use only as active pokemon. This means that my opponent will probably be able to KO very fast the poor "attacking but not damaging" pokemon. I can see that there could be some peculiar circumstances where you could risk to put such a weak Pokémon in attack but I wonder if I am missing something since these very weak Pokémon seem to be rather common.
Ps by the way in the specific case of Cosmog/Cosmoem in my son's deck, the base version seems much more useful since at least draws a card... But as it stands both the base and the evoluted version stand helpless to take hits by the opponents and appear very useful for letting the opponent draw their prize cards...

Can you explain the downvote? If it is a FAQ which is answered on the site I will be more than happy to read it there and if the community so prefer, delete this... I was unable to find it unfortunately until now

There is no recent Cubone that would have no attack that does damage, which one you have in mind?

Sorry got confused with similar names. I was thinking to Cosmog/cosmoem. Will edit for clarity.

They might be just weak cards designed as a filler for an expansion, but most of the time those cards can further evolve into much stronger Pokémon.
Speaking about Cosmog and Cosmoem, those cards mimic their console game counterparts where they are small and mostly useless. But Cosmoem is able to evolve into either Solgaleo or Lunala which are both strong lengendary Pokémon. In TCG, you can evolve in either of them without any limitation.
Here are all the cards Cosmoem can evolve into as of April 2019, you can see that they are nowhere near being useless:

Thanks, my son actually has a Lunala. So the straightforward strategy, barring special circumstances,  would be to evolve them while on the bench and only bring them to attack when they are evolved?

Yes, that's right


text:
Rialto starting player and initial order on Doge track
I have a Czech localisation of Rialto, and I am confused about the initial order on the Doge track. Assume a game of 3 players, with Blue the starting player, followed by Red and then Yellow.
Reading the rules of "Preparing the game, point 11", I see:

Beginning with the starting player, place one of your marker tokens on the starting square of the Doge track."

(Translation mine)
Thew way I understand this, the Blue player will place his marker first, then Red on top of him, and then Yellow on top of them both. So the starting player will be last on the Doge track, and the last player will be leading the Doge track.
However, this feels wrong, since that way, the starting player is penalised in everything:

According to point 14, the starting player gets the smallest number of coins: the starting player takes coins first, and number of coins taken by successive players increases.
According to point 15, the starting player is the last to choose a building, and so has the least choice: the order of choice is specified to start with the player to the right of the starting player, and proceed counter-clockwise.
Once play starts, cards are chosen according to the order on the Doge track, so the starting player is last again and has the least choice.

To add to my confusion, the illustration demonstrating an initial setup has the Blue player holding 1 coin and being the topmost marker on the Doge track.
What are the rules actually supposed to say? Is this a mistranslation of the Czech localisation, or is the starting player really the worst position to be in?

I found a copy of the English rules, and point 11 reads of the setup reads as follows:

Beginning with the player to the right of the starting player and in counter-clockwise order, each player puts one counter on the first space of the Doge track.See below for details on the Doge track.

This would produce the opposite order of yours.
BoardGameGeek has a file titled "Official Czech Rules with corrections." Step 11 of that document reads as follows:

Postupně od hráče po pravici začínajícího hráče a dále
  proti směru hodinových ručiček umístěte své označovací kameny
  na počáteční pole stupnice vlivu dóžete (více o stupnici vlivu dóžete
  najdete níže na této straně).

The quoted passage is in red, which has been used to identify the corrections.
This matches the the text of the English rules I quoted above.

Wow, that correction precisely addresses my question. I browsed BoardGameGeek forums before asking this, but as I am not familiar with that site, I didn't know there could be files for download.


text:
How to Mitigate Snowball Effect of Events
I enjoy the events thematically, but the majority of them seem to be of the general form: Make a [stat] roll. If you succeed, increase [stat], if you fail, decrease [stat].
Because the number of dice you get to roll are based on your current stat value, you're more likely to succeed and increase some stat that you're already good at, and more likely to fail and decrease some stat that you're already bad at.
Especially during the exploration phase, there is little to do except explore new rooms and get hit with unpredictable events which will increasingly cripple you if you have a lower-than-average stat.
Does anyone know of a way to mitigate this snowball effect, so you're not perpetually punished for having a bad roll early?
Edit: More specifically, I was looking for additions to the rules that provide a little more agency/forgiveness than conservative gameplay, which tends to rely on the cooperation of others.

Only 5 of the 45 Event cards (as far as I can see) force stat penalties on the same stat as the initial roll. Most deal physical or mental damage, meaning you almost always have two stats to choose from when taking the hit.

Interesting; I thought it was more common than that, but maybe my roommate has phenomenally bad luck. Maybe it's some of the rooms (like the Junk Room, I believe it's called) which contribute to this feeling.

There are a couple of things you can do to make it less likely you'll get crippled:

Pick a character with balanced starting stats - Brandon Jaspers, Peter Akimoto, Jenny LeClerc and Madam Zostra all start with three of their stats on 4 and the 4th on 3.
When a room that boosts your stats (Chapel, Gymnasium, Larder, Library) appears, make your way there immediately if the haunt hasn't started yet (if the haunt has already started you may have more important things to do).

While I love the game it is pretty random and you have to accept that sometimes you get screwed. It's worth pointing out that you can't die until the haunt starts, in case you missed that rule.

Glad that you brought up that you can't die until the haunt starts. And once it does, there is a good chance that the traitor, if there is one, has also been affected by reduced stats, which helps the investigators.

It's not much better to be one stat above dead when the haunt starts. And it's not in the best interests of the person who discovers a stat-boosting room to wait for everyone else to be able to access it; maybe my group is too selfish from the get-go.

@HammerBro., it's common for the person who finds the stat-boosting room to keep exploring. But, if all of the other players immediately stop exploring to rush to the stat-boosting room, then it's unlikely that the single exploring player is going to start the haunt. All players might not get to all stat-boosting rooms before the haunt starts, but most players should get to most of the stat-boosting rooms.


text:
How are you supposed to build space marines in 8th Ed?
I've been playing Warhammer 40,000 since the last year of 7th Ed and I've had some extreme problems with Space Marines since the swap. While the army was still in 7th Ed, it worked great: 3+ or 4+ saves all around, lots of boots on the ground, could reach out and touch just about anything that i came up against (aside from Belial cheese lists) to the extent that i won about as many games as i lost. With the change to 8th Ed they lost about all of their advantages: AP reduces the armor saves instead of ignoring them on certain thresholds, the detachment and price updates reduce the number of units on the table and BOTH of these utterly kill the my ability to reach out and touch whoever-the-heck. I've tried just about everything with these guys; cram a captain, lieutenant, apothicary, ancient and a few command vets into a vehicle and give them multi-meltas while the rest of the army distracted the enemy (didn't work), built a screen of 6 scouts while 3 sniper squads and the rest of the army fired from behind them (didnt work), built an army with deepstriking terminators with Cyclone rockets and chainfists that killed the big stuff while snipers, thunderfire cannons and librarians took on the little stuff (didnt work either). Just about the only useful thing i learned while trying to make these guys work is that StormTalons are a 174 point unit that kills a maximum of 2 units before it's promptly crushed under the shear mass of fire from everything shooting at it.
I spent a good deal of money on my collection and there's simply too much on my person to even THINK about getting anything else, and i truly want to make this army work, so how are you supposed to field the run-of-the-mill Space Marines?

Would this not solely be dependent on your strategy?  Like do you use short range combat or rely heavily on Heavy Bolters and plasma rifles? Im not overly experienced with 40K but I do love spacemarines and believe they are best at range (minus a few ranged units such as assault marines)

Honestly I feel like as statedthis question is too broad to have a proper answer. Are you playing a narrative game? Tournament? Friendly Matched play?
What army are you playing against? Do you need to WAAC? What models do you have? Which units do you like? There is no single army list that is "correct" and even if you come up with a list that seems to always work, either someone else will come up with a counter or it's the ONLY thing anyone will play and it'll get nerfed.

TLDR, Have around 7 units for every 1000pts and give each unit at least 3 things that make them threatening
I'm writing this because I'm sick of waiting for someone else to answer this and I recently found A way to play Space Marines, though it's highly possible that it's not THE way to play Space Marines. Whatever the case, if this answer gets around 10 votes before someone else writes something and is right, then this will be my accepted answer.
Back to what my findings were, I believe that for every 1000pts, there should be 7 units in the formation and each should have at least 3 qualities or weapons given to them that make the opponent take notice of them. For example, you can give a scout squad shotguns, camo cloaks and a Landspeeder Storm. Instead of "just a unit of scouts" this unit becomes "a Toughness 5/Wound 7 model that moves 18" base, has fly, shoots up to 13 Strength 5 shots plus d6 Srength 4 shots on most turns and spawns up to 5 Scout Marines with a 2+ Save in cover when it dies". Attaining enough units that either have extended descriptions like this, or produce immediate reactions like a Landraider, creates a psychological advantage to your army I like to call The Actuality Effect. The Actuality Effect hinges on how effective your army is despite taking losses, such as a 10 man unit of Devastators loosing 5 units but still having its maximum output of heavy weapon shots. As for the effect itself, it is a mounting stress that occurs when the opponent is loosing units and is dealing seemingly ineffective damage to you. It's crucial to steadily build this tension in your opponent because, like in most strategy games, stress is the great obstacle your opponent must overcome. Stress makes you forget things, makes you focus on some things over other things, pushes you to chase or flee certain situations. Having enough units on the board, ergo unique places that DEMAND your opponents attention, will be enough to tip the odds in your favor.
Since building my lists this way, I haven't lost my last 3 games (2 vs Blood Angels, 1 of which heavily used Primaris units, 1 vs Orks). I won't guarentee that this works 100% effectively, one of my wins left me with 8 models on the board, but it performs drastically better than any of my previous lists this edition. Weather or not this is the best way to play Space Marines in general will be decided in time.

I have been pretty successful with my space marines lately.
TLDR - crimson fists - whirlwind ftw - command points
Here is the list I ran this past week at 1250 points.
crimson fists-
jump pack cap w/burning blade,
cap,
lietentant,
5 man tac w/heavy bolter,
5 man scout w/heavy bolter,
5 man scout all snipers,
7 man terminator w/assault cannon,
razorback w/twin heavy bolter, sb, hk,
2x whirlwind w/ castellan launchers, storm bolter, hk,
venerable dreadnought w/ missile launcher and twin lascannon.
running the captain/lieutenant combo or a chapter master has been devastating. whirlwinds have also been my saving grace. I've been fighting armies with mostly longer range guns than me. The 5ft 4d6 s6 shots rerolling 1s on hits and on wounds that don't require los *all for 103 points!! Tenderizing gunlines while I get into range. Throw in the venerable dread that hits on 2's with rerolls = 97% accuracy.
Heavy bolters with the hellfire shells has helped deal out mortal wounds to armor. and the bolter drill on a terminator deepstrike has netted me 3-5 bonus shots on that list being 30ish stormbolter and 6 assault cannons.


text:
Does this Go-like game have a name?
I remember playing a slightly Go-like game in primary school, using pen and paper. Both players have a pen of their own color (typically pencil and ballpoint) and take turns drawing dots at intersections of a rectangular grid. We called it Pistepeli ("point game" in Finnish) but Google doesn't find anything relevant with that name.
The objective is to surround some of the other player's dots, gaining a point for each one. This is done by completely encircling them, drawing a winding line connecting your own adjacent dots (along the 8 compass directions), only when you have managed to place all the required dots so the line will loop back to its starting point. You may not use your own dots that the opponent has already encircled, but you may re-use your own lines to draw an encircled area next to an existing one.
You may enclose as many areas as you can during your turn, after placing a dot. The game continues until time runs out or there's a dot at every intersection on the paper, and then the game is scored by counting opponent dots each player has surrounded.
I can't remember if there was a rule that drawn dots must be next to an existing dot or specifically also of the opposite color, and how edges of the playing area were treated. Possibly it was forbidden to surround your own dots and/or empty intersections.

In English, this game is called, appropriately enough, Dots.
There is a wikipedia page describing the game and showing an example of gameplay.

That's it! The name made it hard to find with search engines.