text:
What is the strategy called which forces opponents to discard cards?
In MTG: Arena I've built a Rakdos deck with the main strategy of making my opponent discard one or more cards—each turn if I'm lucky. I'm using cards such as Burglar Rat, Fell Specter, Davriel, Rogue Shadowmage and Carnival // Carnage.
Decks that let opponents put the top cards of their library into their graveyard, are often referred to as 'mill decks' or 'milling'. Is my deck a type of milling, or does it have its own term?

First, I want to note that "mill" as a deck strategy name is just named after "mill", which is the common unofficial (now official) name for the action of putting cards into the graveyard from the library. Following that pattern, the name of a discard strategy would just be "discard"
Discard alone generally isn't a strategy because it doesn't actually win you the game. Once your opponent's hand is empty, they can usually play the card they draw each turn before you have a chance to make them discard it.
Decks built around effects like Davriel's triggered ability can be called "rack decks", after the original card with that kind of effect, The Rack, though that fits better with decks that actually play that card. For example, 8-Rack is a commonly recognized name of a deck archetype that plays 8 cards with that kind of effect.

I am not sure about your first point there Murgatroid, mill being named for the common unofficial name of taking cards from deck to graveyard. I think we have a chicken or the egg situation here, where like Cygnus says, the name for the action and deck strategy may have come from the card Millstone originally.

@Andrew Enhanced my answer to include a link to a MTG article where they state that Mill actually comes from the card

I agree that the "mill" action is named after the card Millstone, but it seems very unlikely that Millstone itself was ever the core of a deck with that strategy, because its effect is so weak.

@murgatroid99 it's not that uncommon for unofficial names to come from the first card that had the ability (as I believe the revised millstone is here) or the common thread in early cards that have the ability (as hexproof was originally called "troll shroud" before it was keyworded.)

I'm aware of that. As I said, I agree that the mill action is named after the card Millstone. But people are aware of the action "mill" even without being familiar with the card, so the name of the action has taken on a kind of life of its own. As a result, I think there is a meaningful difference between saying that the deck archetype is named after the action, and saying that it is named after the card.

Is my deck a type of milling, or does it have its own term?

Some Google search (here also here) seem to indicate that the term used is "Discard Deck"...
Those terms are more informal than official. For example, the term "mill" historically comes from the card Millstone, which had an effect of putting cards from the library into the graveyard (as explained in this MTG article).
As you see, it was an informal term that rose from such card... as your deck's strategy is to discard it would follow that it is called a "Discard Deck".

Not really, but then making your enemy discard isn't generally a discrete strategy in MTG. It helps you win by denying them options, but doesn't actually move directly towards a win condition itself like Mill (drawing from an empty deck) or aggro (lots of direct combat damage). Generally discard options form part of a strategy, not the whole strategy. Generally decks that focus on discard use effects that punish it, or less likely lets them benefit from it. For example:

Megrim: Damage to punish discarding
Liliana's Caress: Same as Megrim but loss of life
The Rack: Punishes players with damage for having too few cards in hand
Shrieking Affliction: same as The Rack but loss of life

Some decks that focus on discard this way also speed the game up by running added draw, cards like Howling Mine, sometimes with the extra draw forcing more discard too, with Anvil of Bogardan, making sure there are cards there to discard, since if you focus too much on discard, a player ends up with no cards in hand and is able to play the one card they draw each turn pretty consistently while your discard spells are just dead in your hand. Drawing can be punished in these decks too, with cards like Underworld Dreams.


text:
What happens to a permanent stolen with 'Invoke the Winds' after the thief leaves the game?
Player A steals a permanent from player B, via an effect like Invoke the Winds.
Player A leaves the game.
What happens to the stolen permanent? Does it leave the game as well, and goes in exile of its owner? Or does it go back to the battlefield under its owner's control? Or something else?

Related:
What happens to a permanent I gained control over using Agent of Treachery, and I leave a multiplayer game?
In this example the card mentions

"Agent of Treachery’s effect lasts indefinitely. It doesn’t wear off during the cleanup step, and it doesn’t expire if Agent of Treachery leaves the battlefield. In a multiplayer game, it does expire if you leave the game."

But Invoke the Winds doesn't share that ruling.

Rulings are just clarifications of how the CRs apply to a situation; the presence or absence of a ruling with things using the same wording on the card shoudn't be taken as an indication they behave differently - in fact, it's very common to reference the ruling which exists on a card using the same wording when one is absent on a particular card.

In fact, all that is covered in the accepted answer to the duplicate.

Control of the permanent goes back to player B.
What I can see in the offical rules is 800.4a, which handles a player leaving a multiplayer game. Effects that have given them control of something they don't own immediately end.

800.4a When a player leaves the game, all objects (see rule 109) owned by that player leave the game and any effects which give that player control of any objects or players end. Then, if that player controlled any objects on the stack not represented by cards, those objects cease to exist. Then, if there are any objects still controlled by that player, those objects are exiled. This is not a state-based action. It happens as soon as the player leaves the game. If the player who left the game had priority at the time they left, priority passes to the next player in turn order who’s still in the game.

Notably, it gives us this example:

Example: Alex casts Act of Treason, which reads, in part, “Gain control of target creature until end of turn,” targeting Bianca’s Runeclaw Bears. If Alex leaves the game, Act of Treason’s change-of-control effect ends and Runeclaw Bears reverts to Bianca’s control.

That sounds the most like the example with Invoke the Winds.

Act of Treason lasts until end of turn though, Invoke the Winds doesn't state that. So the way I read it is that in my case there's no ongoing effect that holds control over the stolen card? Doesn't that change the situation?

Do you want to mention how to get into the situation of "Then, if there are any objects still controlled by that player, those objects are exiled."?

@JonTheMon It's covered in the duplicate question

@Lainathiel There is a continuous effect that is giving you control over the stolen card, it just lasts indefinitely.  The fact that Act of Treason's effect ends at EOT and Invoke the Winds' effect doesn't isn't relevant in this situation.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

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text:
When exactly does the commander tax get added?
Does commander tax increase for each time the commander has been cast, or for each time it has been removed from the battlefield?
For example, if an opponent would kill my commander but I manage to let it go back to my hand instead of the command zone, could I avoid that the tax increases? Or does it still count, because it died?

Nitpick: note that "dies" is now an official term in Magic meaning when a creature or planeswalker is put into a graveyard from the battlefield, so in your example the commander did not die. Not super important in this case, but important for understanding various cards like Death Frenzy.

Commander tax increases for each previous time it has been cast from the command zone.

903.8.: A player may cast a commander they own from the command zone. A commander cast from the command zone costs an additional {2} for each previous time the player casting it has cast it from the command zone that game. This additional cost is informally known as the "commander tax."

Note that it has to be cast from the command zone specifically. Destroying a commander, or putting it into exile, doesn't influence this extra cost. So cards that place it into your hand, such as Command Beacon or Alley Evasion (in response to removal), are effective ways to omit the tax increase.

Cards like Yuriko and Dorevi have abilities that allow you to place them from the command zone onto the battlefield without casting them. When you use those abilities it does not add to the commander tax.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How does Octopus Umbra interact with effects that change the base power and toughness of, and counters on, a creature?
Context
My friend plays a Commander deck, lead by Tuvasa the Sunlit:

Tuvasa the Sunlit gets +1/+1 for each enchantment you control.

She's in play and has +2/+2 — not counters — from the two enchantments on his battlefield. Then he plays Octopus Umbra, which reads:

Enchanted creature has base power and toughness 8/8 [...]

and continues in the rulings with:

Octopus Umbra overwrites all previous effects that set the creature’s base power and toughness to specific values. Any power- or toughness-setting effects that start to apply to a creature after Octopus Umbra becomes attached to it will overwrite this effect.
  (2018-07-13)
Any power- or toughness-modifying effects (those that give +N/+N, for example) and counters will apply to the creature’s new base power and toughness, even if they started to apply before Octopus Umbra became attached.
  (2018-07-13)

A judge explained to him that, when playing the umbra,  every effect prior to playing the umbra disappears, and the new base power and toughness becomes 8/8. He explained that it has to do with the order of layers, which is still new and relatively confusing to myself and our table.
Now after reading the rulings, I'm confused about the "everything gets removed" part. How about Tuvasa's "passive" ability, which increases her P/T due to the amount of controlled enchantments? Isn't that checked constantly, making Tuvasa a 8/8 with +3/+3 from the enchantments?
Did we misunderstand the judge? Or is there something else we're missing? Any clarification would be much appreciated.
Question, in short

In this scenario, what is Tuvasa's power and toughness when playing the umbra? Please take in consideration the example where the umbra itself will be the third enchantment on his battlefield.
Do counters stay on the permanent when enchanting it with Octopus Umbra? Say Tuvasa also had a +1/+1 counter before the umbra came into play. My guess is that the counter stays, since they are placed on top of the base P/T, but I can't find the rules which support or contradict this.

The explanation the judge gave you was unnecessarily confusing.  Nothing disappears or gets removed. Some things get overwritten, but they're still there.

With three total enchantments out, one of them being Octopus Umbra enchanting her, Tuvasa the Sunlit will be 11/11. This is from her base power toughness being 8/8, and from her getting +3/+3 from her ability.
The +1/+1 counter would stay. In the same scenario, if she also had a +1/+1 counter on her, Tuvasa will be 12/12.

What's the layer system doing for us here?
Lots of us struggle with the layer system; it's fine that you are too. The layer system is defined rule 613, Interaction of Continuous Effects.
To know what Tuvasa is going to look like, first let's take a look at how the layers are going to apply the effects in this scenario. In particular we're working with layer 6 (ability-adding effects) and 7 (power/toughness effects).
Layer 6:

Octopus Umbra gives Tuvasa a new ability (“Whenever this creature attacks, you may tap target creature with power 8 or less.”):

613.1f Layer 6: Ability-adding effects, ability-removing effects, and effects that say an object can’t have an ability are applied.

Layer 7: This layer has a whole section covering how to apply it (rule 613.3) so we'll work through that too.

Octopus Umbra sets Tuvasa's base power/toughness:

613.3b Layer 7b: Effects that set power and/or toughness to a specific number or value are applied. Effects that refer to the base power and/or toughness of a creature apply in this layer.

Tuvasa's own ability increases her power/toughness:

613.3c Layer 7c: Effects that modify power and/or toughness (but don’t set power and/or toughness to a specific number or value) are applied.

Tuvasa might also have a +1/+1 counter:

613.3d Layer 7d: Power and/or toughness changes from counters are applied. See rule 122, “Counters.”

Now let's apply those layers.

Layer 6: Tuvasa the Sunlit gains her ability (“Whenever this creature attacks, you may tap target creature with power 8 or less.”). This doesn't affect the rest of our calculations.
Layer 7b: Tuvasa normally has base power/toughness 1/1. We'll now set it to 8/8.
Layer 7c: Tuvasa is currently an 8/8. Her ability gives her a further +3/+3. This would make her now an 11/11.
Layer 7d: Tuvasa might have a +1/+1 counter on her, which would further increase her to 12/12.

Thus our result: Tuvasa looks the same but has an additional ability and is 11/11 or 12/12.
I believe when the judge said "everything prior to the effect disappears", he was referencing the ability for the layer system to result in overrides. Tuvasa's power/toughness was overwritten. If Tuvasa was enchanted with both Kenrith's Transformation and Octopus Umbra, the layer system would tell you the most recent one "wins", overwriting the other to set Tuvasa's P/T to either 3/3 or 8/8. Both effects would still be there and neither would have disappeared, just one would be overwritten.

The judge's ruling was correct. The various modifiers to power and toughness are applied in layers, and the 8/8 base P/T are in a different layer than the +1/+1 for each enchantment. With the three enchantments in your scenario (Octopus Umbra plus two others), Tuvasa the Sunlit will be 11/11 overall.
There are many continuous effects that can modify objects. They are applied in layers. Effects that modify power and/or toughness are applied in layer 7, and layer 7 has another 5 sub-layers. They are applied in the following order:

613.3a Layer 7a: Effects from characteristic-defining abilities that define power and/or toughness are applied. See rule 604.3.

Example: "This creature's power is equal to the number of knights you control".

613.3b Layer 7b: Effects that set power and/or toughness to a specific number or value are applied. Effects that refer to the base power and/or toughness of a creature apply in this layer.

7b is where the 8/8 modifier from Octopus Umbra is applied. It overwrites its original 1/1.

613.3c Layer 7c: Effects that modify power and/or toughness (but don’t set power and/or toughness to a specific number or value) are applied.

7c is where the +1/+1 per enchantment from Tuvasa the Sunlit is applied.

613.3d Layer 7d: Power and/or toughness changes from counters are applied. See rule 122, “Counters.”
613.3e Layer 7e: Effects that switch a creature’s power and toughness are applied. Such effects take the value of power and apply it to the creature’s toughness, and take the value of toughness and apply it to the creature’s power.

Can you please state explicitly what is the P/T in the end? Thanks :)

Tuvasa would be an 11/11 after all is said and done (8/8 + 2/2 from previous enchantments + 1/1 for Octopus Umbra (since it's an enchantment too)).


text:
Interaction between Leonin Warleader and Divine Visitation
I have Divine Visitation on the battlefield:

If one or more creature tokens would be created under your control, that many 4/4 white Angel creature tokens with flying and vigilance are created instead.

Then I play Leonin Warleader:

Whenever Leonin Warleader attacks, create two 1/1 white Cat creature tokens with lifelink that are tapped and attacking.

So the tokens will transfrom into 4/4 angles. But are they still tapped and attacking, or do the angles coming onto the battlefield negate the detail of "tapped and attacking"?
In other words, does the enchantment place the angles instead of:

"Cat creature tokens with lifelink", or
"Cat creature tokens with lifelink that are tapped and attacking"?

related: https://boardgames.stackexchange.com/questions/35348/does-doubling-season-creates-attacking-tokens-with-hanweir-garrison/35349#35349


text:
Does the Tribal card type have inherent mechanical implications?
Research
(emphasis mine)

308.: Tribals
308.1.: Each tribal card has another card type. Casting and resolving a tribal card follows the rules for casting and resolving a card of the other card type.
308.2.: Tribal subtypes are always a single word and are listed after a long dash: "Tribal Enchantment - Merfolk." The set of tribal subtypes is the same as the set of creature subtypes; these subtypes are called creature types. Tribals may have multiple subtypes. See rule 205.3m for the complete list of creature types.

Creature Type: A subtype that's correlated to the creature card type and the tribal card type. See rule 302, "Creatures," and rule 308, "Tribals." See rule 205.3m for the list of creature types.
Tribal: A card type. Whether or not a tribal is a permanent depends on its other card type. See rule 308, "Tribals."

Following these rules, I don't know how to interpret the Tribal card type. So it's not always a permanent (in contrast to creatures). What does the Tribal add to a card as information regarding game mechanics? It comes across as a flavor of cards that doesn't have mechanical connotations, but that strikes me as odd—knowing the wording of MTG (so far in my experience). What am I missing here?
Examples
Let's take Eldrazi Conscription, which is a

Tribal Enchantment - Eldrazi Aura

and compare it to Archetype of Aggression, which is an

Enchantment Creature - Human Warrior

So in this case, both cards are a permanent because they're enchantments (in contrast to All Is Dust). The Tribal type confuses me. It does mention Eldrazi, which is a creature, but the card type doesn't say it is a creature. My intuition tells me that an Eldrazi Aura can only enchant Eldrazi creatures, but the card simply states

Enchant creature

so that means my intuition it wrong.
Does the Tribal card type have inherent mechanical implications, other than not always being a permanent?

To directly answer the question (since none of the questions do): No, Eldrazi Conscription is not a Creature. It can't attack, for example. The Tribal type is simply a hack that allows non-Creature objects to have a Creature subtype.

Tribal came about because of this rule

205.3d An object can’t gain a subtype that doesn’t correspond to one of that object’s types.

Which meant that when Wizards wanted to make instants, sorceries, enchantments, etc. with creature subtypes, they couldn't.  At least, not easily.  Tribal was a work around.  By adding the Tribal type, it allowed Wizards to do an end run around their rules without having to rewrite their rules (I can only imagine what weird edge cases would crop up if any card type were allowed to have creature subtypes).
For reference, there are only certain subtypes a card with a certain type is allowed to have.

205.3. Subtypes
205.3a A card can have one or more subtypes printed on its type line.
205.3b Subtypes of each card type except plane are always single words and are listed after a long dash. Each word after the dash is a
  separate subtype; such objects may have multiple types. Subtypes of
  planes are also listed after a long dash, but may be multiple words;
  all words after the dash are, collectively, a single subtype. Example:
  “Basic Land — Mountain” means the card is a land with the subtype
  Mountain. “Creature — Goblin Wizard” means the card is a creature with
  the subtypes Goblin and Wizard. “Artifact — Equipment” means the card
  is an artifact with the subtype Equipment.
205.3c If a card with multiple card types has one or more subtypes, each subtype is correlated to its appropriate card type. Example:
  Dryad Arbor’s type line says “Land Creature — Forest Dryad.” Forest is
  a land type, and Dryad is a creature type.
205.3d An object can’t gain a subtype that doesn’t correspond to one of that object’s types.
205.3e If an effect instructs a player to choose a subtype, that player must choose one, and only one, existing subtype, and the
  subtype must be for the appropriate card type. For example, the player
  can’t choose a land type if an instruction requires choosing a
  creature type. Example: When choosing a creature type, “Merfolk” or
  “Wizard” is acceptable, but “Merfolk Wizard” is not. Words like
  “artifact,” “opponent,” “Swamp,” or “truck” can’t be chosen because
  they aren’t creature types.
205.3f Many cards were printed with subtypes that are now obsolete. Many cards have retroactively received subtypes. Use the Oracle card
  reference to determine what a card’s subtypes are. (See rule 108.1.)
205.3g Artifacts have their own unique set of subtypes; these subtypes are called artifact types. The artifact types are Clue, Contraption,
  Equipment (see rule 301.5), Fortification (see rule 301.6), Treasure,
  and Vehicle (see rule 301.7).
205.3h Enchantments have their own unique set of subtypes; these subtypes are called enchantment types. The enchantment types are Aura
  (see rule 303.4), Cartouche, Curse, Saga (see rule 714), and Shrine.
205.3i Lands have their own unique set of subtypes; these subtypes are called land types. The land types are Desert, Forest, Gate, Island,
  Lair, Locus, Mine, Mountain, Plains, Power-Plant, Swamp, Tower, and
  Urza’s. Of that list, Forest, Island, Mountain, Plains, and Swamp are
  the basic land types. See rule 305.6.
205.3j Planeswalkers have their own unique set of subtypes; these subtypes are called planeswalker types. The planeswalker types are
  Ajani, Aminatou, Angrath, Arlinn, Ashiok, Bolas, Chandra, Dack,
  Daretti, Davriel, Domri, Dovin, Elspeth, Estrid, Freyalise, Garruk,
  Gideon, Huatli, Jace, Jaya, Karn, Kasmina, Kaya, Kiora, Koth, Liliana,
  Nahiri, Narset, Nissa, Nixilis, Ral, Rowan, Saheeli, Samut, Sarkhan,
  Serra, Sorin, Tamiyo, Teferi, Teyo, Tezzeret, Tibalt, Ugin, Venser,
  Vivien, Vraska, Will, Windgrace, Wrenn, Xenagos, Yanggu, and Yanling.
205.3k Instants and sorceries share their lists of subtypes; these subtypes are called spell types. The spell types are Arcane and Trap.
205.3m Creatures and tribals share their lists of subtypes; these subtypes are called creature types. The creature types are Advisor,
  Aetherborn, Ally, Angel, Antelope, Ape, Archer, Archon, Army,
  Artificer, Assassin, Assembly-Worker, Atog, Aurochs, Avatar, Azra,
  Badger, Barbarian, Basilisk, Bat, Bear, Beast, Beeble, Berserker,
  Bird, Blinkmoth, Boar, Bringer, Brushwagg, Camarid, Camel, Caribou,
  Carrier, Cat, Centaur, Cephalid, Chimera, Citizen, Cleric, Cockatrice,
  Construct, Coward, Crab, Crocodile, Cyclops, Dauthi, Demon, Deserter,
  Devil, Dinosaur, Djinn, Dragon, Drake, Dreadnought, Drone, Druid,
  Dryad, Dwarf, Efreet, Egg, Elder, Eldrazi, Elemental, Elephant, Elf,
  Elk, Eye, Faerie, Ferret, Fish, Flagbearer, Fox, Frog, Fungus,
  Gargoyle, Germ, Giant, Gnome, Goat, Goblin, God, Golem, Gorgon,
  Graveborn, Gremlin, Griffin, Hag, Harpy, Hellion, Hippo, Hippogriff,
  Homarid, Homunculus, Horror, Horse, Hound, Human, Hydra, Hyena,
  Illusion, Imp, Incarnation, Insect, Jackal, Jellyfish, Juggernaut,
  Kavu, Kirin, Kithkin, Knight, Kobold, Kor, Kraken, Lamia, Lammasu,
  Leech, Leviathan, Lhurgoyf, Licid, Lizard, Manticore, Masticore,
  Mercenary, Merfolk, Metathran, Minion, Minotaur, Mole, Monger,
  Mongoose, Monk, Monkey, Moonfolk, Mutant, Myr, Mystic, Naga, Nautilus,
  Nephilim, Nightmare, Nightstalker, Ninja, Noggle, Nomad, Nymph,
  Octopus, Ogre, Ooze, Orb, Orc, Orgg, Ouphe, Ox, Oyster, Pangolin,
  Pegasus, Pentavite, Pest, Phelddagrif, Phoenix, Pilot, Pincher,
  Pirate, Plant, Praetor, Prism, Processor, Rabbit, Rat, Rebel,
  Reflection, Rhino, Rigger, Rogue, Sable, Salamander, Samurai, Sand,
  Saproling, Satyr, Scarecrow, Scion, Scorpion, Scout, Sculpture, Serf,
  Serpent, Servo, Shade, Shaman, Shapeshifter, Sheep, Siren, Skeleton,
  Slith, Sliver, Slug, Snake, Soldier, Soltari, Spawn, Specter,
  Spellshaper, Sphinx, Spider, Spike, Spirit, Splinter, Sponge, Squid,
  Squirrel, Starfish, Surrakar, Survivor, Tetravite, Thalakos, Thopter,
  Thrull, Treefolk, Trilobite, Triskelavite, Troll, Turtle, Unicorn,
  Vampire, Vedalken, Viashino, Volver, Wall, Warrior, Weird, Werewolf,
  Whale, Wizard, Wolf, Wolverine, Wombat, Worm, Wraith, Wurm, Yeti,
  Zombie, and Zubera.
205.3n Planes have their own unique set of subtypes; these subtypes are called planar types. The planar types are Alara, Arkhos, Azgol,
  Belenon, Bolas’s Meditation Realm, Dominaria, Equilor, Ergamon,
  Fabacin, Innistrad, Iquatana, Ir, Kaldheim, Kamigawa, Karsus,
  Kephalai, Kinshala, Kolbahan, Kyneth, Lorwyn, Luvion, Mercadia,
  Mirrodin, Moag, Mongseng, Muraganda, New Phyrexia, Phyrexia, Pyrulea,
  Rabiah, Rath, Ravnica, Regatha, Segovia, Serra’s Realm, Shadowmoor,
  Shandalar, Ulgrotha, Valla, Vryn, Wildfire, Xerex, and Zendikar.
205.3p Phenomenon cards, scheme cards, vanguard cards, and conspiracy cards have no subtypes.

As far as actual mechanics Tribal adds, the answer is it doesn't.  It was a work around for a very large set of cards and rules that prevented having to change one of the game's most fundamental rules.
(The only thing that it does affect is the stuff pointed out in @erik's answer.)

On its face, the wording of "gain a subtype" doesn't seem to prevent them from printing cards that don't obey that rule (it would just exist, not "gain" the subtype?) but that would probably induce other, strange, consequences.

In addition to the other answers I like to add, that the mere fact that it is a card type, and not a subtype or supertype for example, makes it count for cards like Tarmogoyf
And some other neat combo that you can do because of tribals is to keep on casting Nameless Inversion from your graveyard as many times as you have mana for it when Haakon, Stromgald Scourge is on the battlefield under your control

Some cards care about creature types on cards, e.g. Vanquisher's Banner (but that one only cares about creature spells). Door of Destinies on the other hand cares only about the type - it doesn't have to be a creature spell. So if you say Eldrazi as Door of Destinies enters the battlefield, and later cast All is Dust, you put a charge counter on Door of Destinies.

This has nothing to do with the Tribal type directly, only indirectly as non-creature spells with creature subtypes also always have the Tribal card type on them.


text:
Is casting a commander from the command zone considered casting a spell?
For example, say I have God-Pharao's Statue in play:

Spells your opponents cast cost {2} more to cast.

Would my opponents have to pay the two extra mana when playing their commander from the command zone?

Yes, they do have to pay extra mana.

903.8. A player may cast a commander they own from the command zone. A commander cast from the command zone costs an additional {2} for each previous time the player casting it has cast it from the command zone that game. This additional cost is informally known as the “commander tax.”

(emphasis mine)
It's a creature spell, just not cast from their controller's hand as normal.

701.4a To cast a spell is to take it from the zone it's in (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. A player may cast a spell if he or she has priority. See rule 601, "Casting Spells."

701.4b To cast a card is to cast it as a spell.


text:
When a creature is exiled with Nightmare Shepherd, does Teysa Karlov create two copies of the creature when dying?
Example
I have Teysa Karlov and Nightmare Shepherd in play. They mention, respectively:

If a creature dying causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.

Whenever another nontoken creature you control dies, you may exile it. If you do, create a token that’s a copy of that creature, except it’s 1/1 and it’s a Nightmare in addition to its other types.

Then, I sacrifice my Doomed Dissenter:

When Doomed Dissenter dies, create a 2/2 black Zombie creature token.

Confusion
I'm still not sure about replacement effects and whether or not the Doomed Dissenter in this case actually dies, when I choose to let it go into exile to copy it as a token. Because the demon's ability doesn't mention "instead", I think the human still "hits" the graveyard before going into exile. This would mean Teysa does trigger twice, creating two 2/2 Zombies. Does the Nightmare Shepherd also create two copies of the Doomed Dissenter?
This case confuses me, since I can only exile the creature once? But the death trigger still happens twice instead of once? Any clarification would be much appreciated.

You get two 2/2 zombie tokens and up to one 1/1 Doomed Dissenter token.
Both Doomed Dissenter's ability and Nightmare Shepherd's ability trigger twice on Doomed Dissenter's death (i.e. it moved from the battlefield to the graveyard).

700.4. The term dies means “is put into a graveyard from the battlefield.”

These abilities are now on the stack. Dissenter's own ability will resolve, no matter what happens to the Doomed Dissenter card in the graveyard, and you will eventually get 2 zombie tokens.
When it comes to resolving Nightmare Shepherd's ability, assuming you choose to exile the Dissenter card with the first instance, you get a 1/1 Dissenter token. The second Shepherd ability will no longer have a Dissenter card to exile, so that instance does nothing. If you don't choose to exile the Dissenter with the first ability, you can still do so with the second.
There are no replacement effects involved with these cards. None of the abilities have the words "instead" or any other term required for identifying as a replacement effect.

614.1a Effects that use the word “instead” are replacement effects. Most replacement effects use the word “instead” to indicate what events will be replaced with other events.

I know it doesn't use "instead", but Teysa Karlov's ability smells a lot like a replacement effect.

On Teysa it wouldn't make a difference either way, since the death event wouldn't be replaced, only the trigger event. If anything, Nightmare Shepherd's ability might make things interesting if it was a replacement effect.

Note that the "if you do" part is essential here. It says that you only get a token if you exile the card, which is something you can only do once. If it had been left out (as well as the "may", presumably) you would get two tokens.


text:
If I buff an infect card, is the new damage infect as well?
Let's say I have Rogue's Passage and Phyrexian Hydra and I use Rogue's Passage's ability to make Phyrexian Hydra unblockable.  Then, after no spells are played that effect Phyrexian Hydra, I play Titanic Growth on the Phyrexian Hydra. Does the 11 infect kill the opponent that I am attacking as long as no other spells are cast?

Damage has many effects: addition of marked damage, addition of -1/-1 counters, addition of poison counters, loss of loyalty counters, life loss, life gain, a combinations of these, or nothing at all. Whatever the effect, the amount of it is equal to the attacking creature's power.


text:
Does 'counter a spell' mean 'put a creature into its owner's graveyard'?
For example, when I use the card Double Negative, I counter two spells. Does it mean I can put two of my opponents spells (which may be enchantments or creatures) into its owner's graveyard?
I am new to MtG so I might ask stupid questions.

If a spell is on an actual card (e.g. creature, enchantment, instant, etc., usually played from your opponent's hand), then countering that spell means the spell never happens, and the card is moved to its owner's graveyard. (If the spell is not on a card, for instance it's a copy of another spell, then it just disappears.)
Yes, if there are two spells on the stack, Double Negative will allow you to counter both of them, which in a best case scenario means two of your opponents cards are moved to the graveyard, having no effect other than the mana they cost to cast. Note, however, that this will almost certainly require that at least one of them is an instant, as very few non-instant cards may be played while another spell is on the stack (those that do carry the keyword "Flash").
Also note that if your opponent (and you) lets one spell resolve before playing the second spell, then there never were two spells on the stack simultaneously for Double Negative to counter. So if your opponent played a creature, you both let that creature come into play, and he then plays, say, a Shock to deal to damage to you, you can't counter both the Shock and the creature. You lost the opportunity to counter the creature before the Shock was ever a spell.


text:
Are there red cards that offer protection against mass token destruction?
I was playing MtG with a mono red goblin deck, and someone used Virulent Plague on my tokens and they all died! Is there any way to counter this with a mono red card?

What format is this?

Honestly, your options aren't great.  Enchantments are a designated weakness for Red, and as such they have basically no options for dealing with them.
If you search on Gatherer for mono-red cards that have "enchantment" in their rules text, you get only 20 results.  Of those, 3 have off-color activations, 2 destroy nonenchantments, 2 are Licids (which become enchantments), 3 create enchantment creature tokens (they're from Theros), two are a split card with the enchantment destruction on the white side (Gatherer doesn't really handle split cards very well), one only cares about enchantment creatures, 4 have miscellaneous effects that don't help, and one is Warp World.
The only two cards that might possibly be of use to you are Aura Barbs and Enchanter's Bane.  Aura Barbs does a measly 2 damage to your opponent for each Virulent Plague they have (which is terrible), and Enchanter's Bane is only 3 damage a turn, which isn't really a fair trade for shutting down the rest of your deck.  Also, Enchanter's Bane is from a Commander deck, so it's not legal in Modern, if that's what you're playing.
If you dig a little broader you can find some other cards that might work, such as Bearer of the Heavens or Capricious Efreet, but they tend to be expensive and/or random in effect, making them pretty useless for your purposes.
The other classic red solution is to simply win the game before the hoser can wreck their field, but a 3 mana enchantment comes down a little too fast for that to be really viable.
If Virulent Plague is a frequent participant of your local metagame, you're probably going to have to splash white or green if you want your token deck to have a prayer.

In addition to the options provided by Arcanist, there is Chaos Warp, which is the common answer to the question of "can red answer enchantments?".
It isn't standard or modern legal, however, and in general red needs to branch out to another colour to be able to interact with enchantments.
Colourless cards, however, are much better at answering enchantments. They're not strictly mono red and are often high converted mana cost (so may not be particularly helpful in your case), but they are castable with just red mana!
Standard options:
Ugin, the Ineffable
Meteor Golem
Outside standard options:
Ugin, the Spirit Dragon
Karn Liberated
Spine of Ish Sah
Ulamog, the Infinite Gyre
There is also the other option of not destroying the enchantment, but instead making use of its effect. Outpost Siege on Dragons would keep you strictly mono red, and allow you still to make use of your tokens if your opponent has a Virulent Plague in play. They'll enter, die immediately, but ping something for 1 on the way out. It has the advantage of being proactive, good in multiples, and you can choose Khans as a card advantage option.
Another option again is to pump your Goblins to be big enough to overcome the effect with the likes of Goblin Chieftain. This is a card you may want to play anyway, but could itself be removed by your opponent to make their Virulent Plague effective again.

Getting rid of the enchantment after it is on the battlefield may not help with this particular problem; the moment the enchantment resolves it will still kill all of his creatures.

Yeh, I totally agree. I may have taken too much of a "can mono red destroy an enchantment" approach initially. Outpost siege/goblin warchief suggestions are actual strategic suggestions. You are very limited by mono red, but "stop using tokens"/"don't use red" isn't the best answer to "how do I protect my tokens as mono red", so I tried to provide an answer which keeps the main plan as goblin tokens.


text:
I have an Ivy Lane Denizen, how does targeting work?
I have an Ivy Lane Denizen, it says that he may put a +1/+1 counter on target creature whenever a creature enters the battlefield under my control. Does the counter go on Ivy Lane Denizen specifically or on the creature that just entered? Or does "target" mean I choose any creature of my choice?

Cards in Magic: The Gathering (at least when looking at the official Oracle wording, found on Gatherer) usually mean exactly what they say, nothing more and nothing less. If you had to place the counter on the denizen, it would've said "Whenever another green creature enters the battlefield under your control, put a +1/+1 counter on Ivy League Denizen.", and if you had to put the counter on the creature that just came out, it would've said "Whenever another green creature enters the battlefield under your control, put a +1/+1 counter on that creature."
When an ability or spell you play uses the word "target", you are entirely free to choose a target to your liking, within any explicitly mentioned restrictions (it has to be a creature since it says "target creature", said creature can't have shroud or protection from green, etc.)

Knowing that the card means exactly what it says isn’t helpful in this case if you don’t know what “target” means. So I don’t think the summary a good one here. I think the second paragraph is the important part; the OP didn’t seem to know that “target” has anything to do with making a choice.

You can put the counter on any creature you desire. So it can be Ivy Lane Denizen, creature that entered the battlefield, one of your other creatures or even one of your opponent's creatures. You need to be able to target that creature, though.

"Target" means that you get to choose what object is going to be affected by your spell or ability. You make this choice when you cast the spell or when the ability is activated or triggered.
"Target creature" means that you must choose a creature.
From the MTG Basic Rulebook:

Casting a spell

If the spell is an instant or sorcery and it has a target , you choose what (or who) that target is.

and

Target

When you see the word “target” on a spell or ability, you have to choose one or more things for the spell or ability to affect. You’ll be able to choose only
    certain kinds of things, such as “target red permanent” or “target creature or player.”
You choose the targets for a spell when you cast it, and you choose targets for an activated ability when you activate it.

The rules for selecting targets for a triggered ability, such as Ivy Lane Denizen's ability, work the same as for casting a spell or activating an ability.

Magic is a game where wording matters a lot. You found two very important and common wordings in cards in this one card we are talking about.

Whenever another green creature enters the battlefield under your
  control, put a +1/+1 counter on target creature.

Let's dig in as this will help you understand other rulings in the future.
The first word that matters to you here is "When", this gives you an indication of a triggered ability, something happens when something else happens.
Now we know that a trigger happens, what kind of trigger is it? "enters the battlefield". So now we know what will cause it to trigger, when something enters the battlefield. but we need to know what the something is. So the condition for this ETB (enters the battlefield) trigger is "another green creature". The creature has to be green and has to be another, so it means that this won't trigger when Ivy Lane Denizen itself enters the battlefield, at least for its own triggered ability.
Now your question is about the targetting part of the ability.
There is quite a bit you can read about targetting on the comp rules but in this case use the same logic as we used for the ETB side. So we know what causes it to trigger, now we need to know what effect the trigger brings. The trigger makes you target something. The something in this is creature. And what modifier condition is there for creature? None. In this case, in this card, the only condition for the target is that it has to be a creature (and the target be legal). if, just like the ETB it said "another" creature, then this would be the modifier for the condition.
Mostly, rules on MTG cards are as simply as the text in the card, there is no need for interpretation. Always use the gatherer for clarification, but I would suggest trying to find the solution yourself first.


text:
What is the priority sequence during a turn?
I know that at the beginning of each step and phase the active player recieves priority, and that the active player recieves priority after a spell resolves. I want to make sure that I am right about getting priority during a turn. Please tell me if I'm right and correct my mistakes.

Beginning phase:

Untap step: nobody can casts spells
Upkeep step: players get priority in order of active player, nonactive player
Draw step: the same as in upkeep

First main phase:

active player has priority during the entire turn and nonactive gets it after active passes, at the end of the turn

Combat phase:

after every step players get priority in order active player, nonactive player

Second main phase:

the same as in first

End phase

End step: players get priority in order active player, nonactive player
Cleanup step: nobody can cast spells

Please create a separate question for your second question; this site works off of having one question per post.

You seem to have things basically correct, but some of your wording is confusing; especially as it relates to the main phase.
You say that the active player gets priority "during entire turn" and that non-active player gets it after active passes, "at the end of the turn". Priority in the main phase works exactly the same as it does in the other phases and steps... active player gets priority first, and when active player passes priority, non-active player gets priority.
You are correct about which steps don't give players priority: untap step and cleanup step are the only ones; during all other steps the active player gets priority, and then non-active player gets priority when active player passes it.
Note that in many steps; something else happens before players receive priority, such as drawing a card in the draw step; declaring attackers in the declare attackers step, etc.

Note that players can get priority during the cleanup step,  but only if cleanup causes abilities to trigger or state based effects to occur.  After that there will be another cleanup step, so you're guaranteed to have exactly one cleanup step where nobody received priority.

@Arcanist Lupus Yeah, I think that needs to be added for clarity here.  The most common way for this to happen is to have a buffed creature with -1/-1 counters (or any -X/-X continuous effect that lasts past the end of the turn) that loses the buff during cleanup.  A more recent Standard example is to use the +1 from Sarkhan the Masterless, then activate a loyalty ability of one of those temporary dragons that uses up all of the loyalty counters.  There are also the former "substance" cards that specifically trigger on cleanup for rules reasons such as Armor of Thorns.


text:
What happens when Teysa Karlov is equipped with Helm of the Host?
What happens when you equip Helm of the Host to Teysa Karlov? Do the Teysas trigger each other making infinite copies of the death trigger? My thinking is that it says: when a triggered ability is caused by death, copy it. Is that ability copied by the other Teysa or is the original ability just copied again? So instead of one Blood Artist trigger, would I get 3? Or would I just win the game doing infinite damage?

You get one more trigger for each Teysa Karlov you have. So if you have 2 Teysa Karlov, you get 3 triggers.
From the Rulings on the Gatherer page:

1/25/2019 — If you somehow control two Teysas, a creature dying causes abilities to trigger three times, not four. A third Teysa causes abilities to trigger four times, a fourth causes abilities to trigger five times, and so on. This also means that if you control Teysa and cast a second one, an ability that triggers when it dies due to the “legend rule” triggers three times.

It works this way because Teysa Karlov's ability is a replacement effect, and replacement effects can only apply to an event once. When a death trigger occurs, one Teysa sees it and replaces it with two death triggers, then the other Teysa sees it and replaces it with three death triggers. Both Teysas have now applied their replacement effects to this one event and can't apply additional times, so they won't loop infinitely.

would you be able to copy the Teysa's ability with strionic resonator

or would you be able to  counter it with Tale's End

Teysa's first ability is a replacement effect (not a triggered ability, activated ability nor legendary spell) a so it cannot be copied with strionic resonator nor countered with tale's end.

Teysa's ability isn't triggered by another creature dying, it's triggered by an ability that's triggered by a creature dying. For instance, suppose a creature has "When this creature dies, gain one life". When that creature dies, its ability is triggered, and "gain one life" is put on the stack. Teysa's ability is then triggered. It's triggered not by the creature dying, but by "gain one life" being put on the stack. Teysa will then put another "gain one life" on the stack, but since this was not triggered by a death, it will not trigger Teysa. Teysa is only triggered when a trigger is specifically from a death, not whenever a death is part of the causal chain that leads to the trigger. If you have an additional Teysa, it will see the original "gain one life" being put on the stack, and this will trigger it putting an additional "gain one life" on the stack. So:
Creature dies.
"Gain one life" put on stack.
One of the Teysas sees "Gain one life" being put on the stack as a result of a death, and so puts an additional "Gain one life" on the stack.
The other Teysa sees "Gain one life" being put on the stack as a result of a death, and so puts an additional "Gain one life" on the stack. The other "Gain one life", however, was not put on the stack from a death, and so does not trigger Teysa.

Teysa's ability isn't a triggered ability at all, and it doesn't get put on the stack. It just causes the original triggered ability to trigger more times at the same time.

I agree this answer has errors. Teysa does not see the ability being put on the stack and then respond. It sees the original ability while it's in the process of being put on the stack because it's a replacement effect, and replaces "put one of these abilities on the stack" with "put two on the stack simultaneously", and then they are put on the stack together.


text:
Could I still play cards from the activated ability of Golos while the Epic effect is active?
Spells cast with the keyword Epic, like Eternal Dominion prevent the player from casting other spells for the rest of the game. However, Golos, Tireless Pilgrim says:

Exile the top three cards of your library. You may play them this turn without paying their mana costs.

Would I be able to use Golos's activated ability and cast cards after using Eternal Dominion?

Epic prevents a player from casting spells through Golos or any other means.
Golos allows you to cast the spells it exiles from exile, but that doesn't matter for Epic. Epic prevents all spells from being cast. Casting a spell from anywhere else than the hand still counts as casting, even though it rarely happens and always requires a card specifically allowing you to do so.

112.1. A spell is a card on the stack. As the first step of being cast (see rule 601, “Casting Spells”), the card becomes a spell and is moved to the top of the stack from the zone it was in, which is usually its owner’s hand.

The keyword here is "usually", which means it doesn't have to be from a player's hand to count as casting. So you can activate Golos's ability, the cards get exiled, but you won't be able to cast the cards it exiles.
Also, in case your question was more about whether Golos' ability overrides Epic by explicitely allowing you to cast spells, then no, it doesn't do that either:

101.2. When a rule or effect allows or directs something to happen, and another effect states that it can’t happen, the “can’t” effect takes precedence.

I could be wrong (I'm new to magic) but land cards are never 'cast' and only played. Does that mean you can still play then using Golos?

@user6916458 Yes, that's correct, for precisely the reason you said. ikegami's answer mentions this explicitly.

Yes, you would be able to activate Golos's activated ability.
No, you couldn't cast cards exiled by Golos's activated ability (but you could play lands exiled by the ability).

Golos's ability instructs you to play a card.  To play a card means to play that card as a land or to cast that card as a spell.[CR 701.13b]
Epic creates a continuous effect that says you can't cast spells for the remainder of the game.[CR 702.49a]
For non-lands, we have a conflict resolved by the second Golden Rule:

101.2. When a rule or effect allows or directs something to happen, and another effect states that it can’t happen, the “can’t” effect takes precedence.

This means the restriction from Epic's continuous effect trumps all instructions to cast spells, including the permission granted by Priority (the normal way of casting spells) and effects from abilities such as Golos's.
If Golos's ability exiles a land, you may play it as a land (subject to the usual timing restrictions and the limit on the number of lands per turn).
If Golos's ability exiles a non-land, you may not play it, as that would involve casting it.

101.2. When a rule or effect allows or directs something to happen, and another effect states that it can’t happen, the “can’t” effect takes precedence.
701.13b To play a card means to play that card as a land or to cast that card as a spell, whichever is appropriate.
702.49a Epic represents two spell abilities, one of which creates a delayed triggered ability. “Epic” means “For the rest of the game, you can’t cast spells,” and “At the beginning of each of your upkeeps for the rest of the game, copy this spell except for its epic ability. If the spell has any targets, you may choose new targets for the copy.” See rule 706.10.

Yes, you can activate the ability. No, you cannot cast the spells you exile.
The Epic ability prevents you from casting any more spells from the rest of the game, regardless of how this occurs. Golos's ability exiles the top three cards of your library and then allows you to cast spells without paying their mana costs for the rest of the turn; since abilities will try to do as much as they can, as a result, if it is activated after casting an Epic spell, you simply exile the top three cards of your library and nothing else happens.


text:
Paying more mana for a Flashed creature
Flash says

You may put a creature card from your hand onto the battlefield. If you do, sacrifice it unless you pay its mana cost reduced by up to 2.

(emphasis mine)
Does this "up to" clause mean that I can choose to Flash something and pay its full mana cost, or that it's only reduced by one?

The use of "up to" means that the discount is optional.  You can chose to have Flash's ability use a generic mana cost reduction of 0, 1, or 2.

Rules justification
The phrase "up to" is consistently used in Magic to mean you get to chose a number between 0 and the full value.  You can choose to have Abandon Reason target 0, 1, or 2 creatures.
See the ruling on Training Grounds (which has a similar cost reduction) for one defense of this:

You may choose not to apply Training Ground’s cost reduction effect. You may also choose to apply only part of it (causing an activated ability of a creature you control to cost just {1} less to activate).

As further defense, the use of "up to" is not necessary to support cards that have less than 2 generic mana in their cost.  Magic in general does not need specific wording to prevent numbers from going negative (see 107.1b Most of the time, the Magic game uses only positive numbers and zero.).  For example, Arcane Melee and Power Artifact do not include the phrase "up to", and yet each reduces costs just fine.

Where this matters
Where the optionality of cost reduction usually matters is with cards like Prossh, Skyraider of Kher or Jeleva, Nephalia's Scourge.  However, this isn't relevant here because Flash is not casting the creatures, and therefore not reducing the mana spent to casting them.  Mana burn was one of the main reasons this would matter; good thing Wizards got rid of that rule :)  For examples of when this would matter, see here: When would it be advantageous not apply Training Ground's cost reduction?

@Arthur There is no mana spent to cast Prossh if you use Flash because Prossh isn't cast.  It's the same as if you had used Elvish Piper.

You can't necessarily use Arcana Melee as justification, because it reduces casting costs - the costs you pay for the Flash effect are not casting costs, so they dont necessarily use the same wording. As Glorfindel has quoted, the ruling for Flash has the example of the 1R creature that "you'll have to pay {R} to keep it".

@Hackworth I included that card-specific ruling in my answer as well as a discussion of it.

How do you explain the ruling then? If the cost reduction was optional, then why do you "have" to pay R to keep an 1R creature? Also, since mana burn has long since been removed, why was Flash not errata'd if mana burn was the only reason?

@Hackworth English is ambiguous "You have to pay {R} to keep it" could mean either "pay exactly {R}" or "pay at least {R}".  "The cost is {R}", meanwhile, is not ambiguous.

This answer appears to be correct based on a ruling on the card Training Ground. Training Ground also uses the phrase "up to" in the context of applying a cost reduction and the ruling says that you can ignore the cost reduction or use only part of it.

@murgatroid99 Great example.  I've added it to my answer

"However, this isn't relevant here because Flash is not casting the creatures, and therefore not reducing their casting cost (because there isn't one)." Those cards check the amount spent to cast them, not the casting cost.  The CMC of Prossh is always 6, regardless of how much is spent to cast it. Also "chose" -> "choose".

"English is ambiguous "You have to pay {R} to keep it" could mean either "pay exactly {R}" or "pay at least {R}"." While English is ambiguous, I don't think MtG is ambiguous in this situation. You can't doing anything in Magic unless there's a rule that says you can. You can't just decide to spent mana without there being something that requires you to spend mana.

@Acccumulation Magic is not ambiguous.  I have three pieces of evidence showing that the cost reduction on Flash is optional.  I mention the card specific ruling, not as piece of evidence in favor of my conclusion, but to show that it is not a piece of evidence against my conclusion.

I'm removing Flash's card specific ruling from my answer because it seems to be causing more confusion than it's clearing up.


text:
Interaction between Leyline of Anticipation and Teferi, Time Raveler
With the reprint of LeyLine of Anticipation in Core Set 2020, the interaction with Teferi, Time Raveler came to mind and I couldn't figure out what is right.
If I have the Leyline and my opponent has Teferi, may I cast spells during my opponent's turn?

@Glorfindel, why people change link from scryfall to gatherer? The links of gatherer always send to a page with "Your search returned zero results; click here if you would like to refine it. Please check your search terms and try again."

Those are the official Magic the Gathering links... For some cards the autolink doesn't work (e.g. if there's an apostrophe in the name), but here they do.

Links to cards on Gatherer don't work properly when your preferred language is set to something else than English or when you are shown the localized website for your area (searching via the search bar still works correctly). For this and other reasons I highly prefer Scryfall over Gatherer. Gatherer is also linked on the Scryfall page, so it's literally just one click away for those who prefer Gatherer.

Leyline of Anticipation won't help you; you will only be able to cast spells on your turn, in your main phases, when the stack is empty.

307.5. If a spell, ability, or effect states that a player can do something only “any time they could cast a sorcery,” it means only that the player must have priority, it must be during the main phase of their turn, and the stack must be empty. The player doesn’t need to have a sorcery they could cast. Effects that would preclude that player from casting a spell or casting a sorcery don’t affect the player’s capability to perform that action (unless the action is actually casting a spell or casting a sorcery).

So "any time they could cast a sorcery" does not mean literally "is it possible to cast a sorcery under the current game conditions". Instead, it means "could they cast a sorcery under the default rules of the game".
When you also have Leyline of Anticipation, you normally are allowed to cast a spell any time you have priority:

304.5. If text states that a player may do something “any time they could cast an instant” or “only as an instant,” it means only that the player must have priority.

However, because this conflicts with the restriction on Teferi, the restriction takes precedence:

101.2. When a rule or effect allows or directs something to happen, and another effect states that it can’t happen, the “can’t” effect takes precedence.

This is confirmed by a ruling on Teferi, Time Raveler:

If an effect allows opponents to cast spells any time they could cast an instant (for example, if your opponent also controls a Teferi, Time Raveler and activates his +1 loyalty ability), the restriction of Teferi’s first ability takes precedence over that permission.

Maybe I'm missing something, but how does this answer the question? You only give the definition of "any time they could cast a sorcery” but even knowing this definition I would say that the question still holds. one card says you can only cast during your main phase, when stack is empty and you have priority and the other card says you can cast whenever you can cast an instant. Why would one effect win over the other?

@IvoBeckers Interesting point... I was thinking about it only from the point of view of "if I can cast something as though it had flash, then does my opponent's turn count as a time that I could cast a sorcery?" Looking to see if there's another rule other than 101.2 I can add.

@IvoBeckers I think it's just in the definition of Flash: "You may play this card any time you could cast an instant." Due to Teferi's ability, your opponent's turn is not a time that you could cast an instant.

i think you're right :)

The part "there is no similar rule" is wrong -- 304.5 is that rule.

@m90 Interesting; is that by any chance an updated/new rule, or did I just miss it?

Trying to edit to fix, but I'm actually unsure of the proper rule now. Does 101.2 apply here, even though the word "can't" is not used in the text? Does "only" count?

@GendoIkari It has existed since at least 2013.

@GendoIkari I believe 101.2 does apply to any restrictive effect (as does 614.17): see, for example, Gatherer's first ruling on Fires of Invention.

No, you can't. In general in Magic, 'can't' beats 'can', and this is no exception. It's explicitly mentioned in the Rulings below the card in Gatherer:

If an effect allows opponents to cast spells any time they could cast an instant (for example, if your opponent also controls a Teferi, Time Raveler and activates his +1 loyalty ability), the restriction of Teferi’s first ability takes precedence over that permission.

I think the crux of the issue here isn't that "can't trumps can", but that the Leyline allows sorceries to be played at instant speed, and thus being restricted by an opponent's Teferi doesn't seem like a restriction. I remember questions about this going all the way back to equipments versus Vedalken Orrery.

Why does the layer/timestamp system not apply?

@Acccumulation “101.2. When a rule or effect allows or directs something to happen, and another effect states that it can’t happen, the “can’t” effect takes precedence.” That rule applies everywhere, including the interaction of continuous effects.

@GendoIkari but "can't" isn't actually mentioned here.

"Cast at sorcery speed" is shorthand for a lot of things. A more technical wording could be "Can't cast spells unless the stack is empty during one of your main phases and you have priority"

Now I'm curious why the templating uses "any time you could cast a sorcery", when it could just as easily use "any time you could play a land" or "any time you could cast a creature" or "any time you could cast an artifact" instead.

Teferi wins, but IMHO, for a different reason. Leyline of Anticipation is giving all of your spells the Flash static ability.

702.8a Flash is a static ability that functions in any zone from which you could play the card it's on. “Flash” means “You may play this card any time you could cast an instant."

Look at Slimebind, or any other card with Flash. If your opponent has Teferi, you can still only cast Slimebind when you can cast a Sorcery. With Leyline, think of it as every spell you have in the game now has the word "Flash" written on it. Teferi isn't nullifying the word "Flash" on your spells. He is affecting when your spells can be cast.

I think the recent add-on to my answer is addressing this same point; at least if I'm reading it correctly. Teferi is changing the meaning of "when you can cast an instant".


text:
Does devoid make a card's color identity colorless in Commander?
Certain Battle for Zendikar Eldrazi cards have:

Devoid (This card has no color.)

According to a video by Mark Rosewater, that means regardless of the colored mana required to cast the card, the card itself is colorless.
So then, just like the example with Extort: even though there are color mana symbols in the reminder text, those do not count towards color identity.
Given this, if I have a colorless Commander (e.g. Kozilek, the Great Distortion, Ulamog, the Ceaseless Hunger, Karn, Silver Golem, etc.), can I include Devoid cards - as they are colorless? I checked various sources and seem to come up with equal support pro and con. The last line of 105.2 reads:

An object’s color or colors may also be defined by a color indicator or a characteristic-defining ability.

Devoid is such a defining ability...

Related: https://boardgames.stackexchange.com/questions/34638/how-do-i-resolve-inconsistencies-between-the-rules-committee-commander-rules-and

No, the reason that you cannot use Devoid cards in a Commander deck with a colorless commander is that a card's "color" is not the same thing as it's "color identity". "Color identity" dictates what cards that can go in your Commander deck, not "color".
Devoid changes a cards color.

105.2. ...An object is the color or colors of the mana symbols in its mana cost...

Devoid does not affect the card's color identity.

903.4. The Commander variant uses color identity to determine what cards can be in a deck with a certain commander. The color identity of a card is the color or colors of any mana symbols in that card’s mana cost or rules text, plus any colors defined by its characteristic-defining abilities (see rule 604.3) or color indicator (see rule 204).

If the rules text for Devoid said "This card's color identity is colorless" then things would be different.

No
Color identity includes the following:

the color or colors of any mana symbols in that card’s mana cost or
rules text, plus any colors defined by its characteristic-defining
  abilities
From the Comprehensive Rules (Commander 2017 (August 25, 2017))

While the card text states that the card is colorless it does include colored mana symbols on the card. These colored mana symbols will determine the color identity of the card.
The example of Extort you give doesn't apply to this because the mana symbol is part of the remainder text but not the mana cost or rules text of the card.

From what I understand, Colour Identity does include anything that uses and displays colours in the game. So for you to be able to have a devoid creature with a colour in its mana cost, it would have to be in your commander's colours. I got this from this article on reddit.
Furthermore, I would think it would be counterproductive to have devoid cards in a commander deck that have different colours than your commander. This is because your mana sources would be limited to devoid sources of that mana and artifacts that produce mana of any colour. Even if a devoid creature ignored the colour identity, most sources of mana for that permanent would have that colour identity and would be illegal in the deck.

that first sentence is not strictly true, reminder text is exempt. for instance the orzhov hybrid mana symbol in extort's reminder text does NOT effect colour identity. Crypt Ghast for instance is a legal card in a mono black commander list.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
After lethal first strike damage to an indestructible creature, will it still do damage?
If I were to attack with a 4/4 indestructible creature and it's blocked by a 4/2 creature with first strike, would my indestructible creature still attack during the second combat damage step, or would it just tap, not assigning any damage?

"or would it just tap, not assigning any damage" - this roughly how regeneration works.

@tsuma534: I believe it's more of a loose way of describing that a creature is tapped in order to attack, but will be somehow prevented from dealing damage due to having received lethal damage.

Indestructible, as with most abilities, doesn't modify how combat works - it only does this:

702.12b. A permanent with indestructible can’t be destroyed. Such permanents aren’t destroyed by lethal damage, and they ignore the state-based action that checks for lethal damage (...).

The respective state-based action that 702.12b renders unaffecting:

704.5g. If a creature has toughness greater than 0, and the total damage marked on it is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed. (...)

This results in the following chain of events:

In the first combat damage step, the 4/2 will deal 4 damage to the indestructible 4/4 creature.
State-Based Actions are checked, but even though the creature has lethal damage marked on it, it won't be put into the graveyard and therefore not removed from combat.
In the second combat damage step, the 4/4 will deal 4 damage to the 4/2.
State-Based Actions are checked, see lethal damage marked on the 4/2, and put into the graveyard.

Your indestructible creature would deal damage during the second damage step. At that point in time, it has 4 marked damage, but since it is indestructible, it is not, well, destroyed.  So, the 4/2 in your scenario would die.


text:
Will Roalesk, Apex Hybrid, trigger Sharktocrab twice?
Sharktocrab reads

Whenever one or more +1/+1 counters are put on Sharktocrab, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

If I were to put two +1/+1 counters on it at once, by playing Vivien of the Arkbow, then its ability would only trigger once.
But what about Roalesk, Apex Hybrid, which reads

When Roalesk dies, proliferate, then proliferate again.

The first ability is placing a counter on Sharktocrab, just like when I use Vivien. But the Roalesk then places another counter separately. Would Sharktocrab therefore trigger twice?

Count the instructions (verbs). Everything an instruction has you do is done simultaneously, but each instruction is performed in turn.

@ikegami though there are exceptions, like drawing multiple cards.

Yes, it would.
Even though no one gets priority in between the instructions "proliferate" and "then proliferate again"; each instruction is still a separate instance, and Sharktocrab's ability will trigger after each of them.
Abilities trigger as soon as the relevant event happens; they don't wait to trigger until an entire ability is done resolving.

603.2. Whenever a game event or game state matches a triggered ability’s trigger event, that ability automatically triggers. The ability doesn’t do anything at this point.
603.3. Once an ability has triggered, its controller puts it on the stack as an object that’s not a card the next time a player would receive priority.


text:
Do artifacts count as creatures when they are put into a graveyard while March of the Machines is in play?
Say I have March of the Machines in play, along with Sunbeam Spellbomb and Salvaging Station. I pay {W} and sac the Spellbomb to gain 5 life. Does the Spellbomb trigger the untap-ability on Station?
I tried to find if this was already answered and found a lot of threads dealing with entering the battlefield, but nothing about leaving it.

TL;DR: Yes, it triggers. Sunbeam Spellbomb stops being a creature once it's in the graveyard, but for the 'leaves the battlefield' it's important how it looks like on the battlefield, not the graveyard.

Salvaging Station's last ability is a so-called 'leaves the battlefield' ability, even though it's printed more like an 'enter the graveyard' ability. However, the current Oracle text of that ability reads:

Whenever a creature dies, you may untap Salvaging Station.

'Dies' is short for something else:

700.4. The term dies means “is put into a graveyard from the battlefield.”

Therefore, it's a 'leaves the battlefield' ability:

603.6c Leaves-the-battlefield abilities trigger when a permanent moves from the battlefield to another zone, or when a phased-in permanent leaves the game because its owner leaves the game. These are written as, but aren’t limited to, “When [this object] leaves the battlefield, . . .” or “Whenever [something] is put into a graveyard from the battlefield, . . . .” (See also rule 603.10.)

Let's have a look at 603.10:

603.10. Normally, objects that exist immediately after an event are checked to see if the event matched any trigger conditions, and continuous effects that exist at that time are used to determine what the trigger conditions are and what the objects involved in the event look like. However, some triggered abilities are exceptions to this rule; the game “looks back in time” to determine if those abilities trigger, using the existence of those abilities and the appearance of objects immediately prior to the event. The list of exceptions is as follows:

(emphasis mine)

603.10a Some zone-change triggers look back in time. These are leaves-the-battlefield abilities, abilities that trigger when a card leaves a graveyard, and abilities that trigger when an object that all players can see is put into a hand or library.

The appearance of the Sunbeam Spellbomb on the battlefield was an artifact creature, so Salvaging Station's ability will trigger.


text:
Was it ever possible to target a zone?
I noticed that MTG has an update to the rules for targeting. I don't know how long ago it was changed (the post containing this rule was from 2015), but there used to be this rule:

114.2 Only permanents are legal targets for spells and abilities, unless a spell or ability (a) specifies that it can target an object in another zone or a player, (b) targets an object that can't exist on the battlefield, such as a spell or ability, or (c) targets a zone.

This rule has now been changed:

115.2. Only permanents are legal targets for spells and abilities, unless a spell or ability (a) specifies that it can target an object in another zone or a player, or (b) targets an object that can’t exist on the battlefield, such as a spell or ability. See also rule 115.4.

Was the "targets a zone" text ever relevant? I am pretty sure that no card currently targets a zone (and if such a card existed, it would be strange to remove that part of the rules). But was there ever an old wording on a card (or just a weird rules situation) where a zone would be targeted?
Note that "target player's library" or "target player's hand" targets the player, not the zone (at least under the current rules).

I think the explanation given for the change was to make hexproof apply in situations where one would expect it to apply (and presumably to satisfy the general push towards simplification).

@ikegami According to the update article, it sounds like it was simply because after Circu received oracle wording to make it consistent with other cards; there were simply no longer any cards that targeted the library.

Re "There were simply no longer any cards that targeted the library", And that was because the cards were changed, and they were changed because ...? The document to which you linked is silent on the matter.

It was only one card, not multiple... this other article talks about why Circu received oracle wording updates; and it was basically just to make it consistent with every other card that interacted with libraries.

Well, it's actually consistent with what I said ""target library" versus "target player's library" was subtle enough that not everyone believed there was actually a difference." A difference --the difference?-- being the situation where players have protection or hexshroud

Funfact: there are cards that say "Enchant world" like Forsaken wastes from the set Mirage.

@TotumusMaximus All such cards have a current oracle wording of "World Enchantment" instead; with World being a super type. Back when "Enchant World" was printed, did such enchantments actually target?

The printed text of Circu, Dimir Lobotomist says "target library". The same rules update that changed the rule you quoted also errata'd that card to say "target player's library".

Thanks! Out of curiosity, did you just happen to know this off-hand, or did you find it through searching?

I actually already knew this. Among people like me who specifically learn about edge cases and weird situations in the rules, this was a fairly well-known example.

Amusingly, being allowed to target a library was created specifically so that Circu could be printed with text of readable size; "target player's library" would have caused each of his first two abilities to require three lines of text instead of two. This is no longer the case now that "exile" is a defined term.

After posting the question, I continued my Google search, and came across this forum post that seems to have the answer.
In addition to change change in 114.2 (now 115.2), 114.1 was also updated from:

114.1. Some spells and abilities require their controller to choose one or more targets for them. The targets are object(s), player(s), and/or zone(s) the spell or ability will affect.[...]

to

114.1. Some spells and abilities require their controller to choose one or more targets for them. The targets are object(s) and/or player(s) the spell or ability will affect. [...]

According to the forum post, only one card ever targeted a zone; Circu, Dimir Lobotomist, which received errata to change it from "Target library" to "Target player's library".


text:
How does Frenetic Sliver interact with the Unearth from Dregscape Sliver?
If I Unearth a sliver with Dregscape Sliver's ability and then use Frenetic Sliver's ability, what happens when I win my coinflip? Does the sliver come back at the end of turn?

A ruling on Dregscape Sliver on Gatherer says

If a creature returned to the battlefield by the unearth ability would leave it for any reason, it’s exiled instead—unless the spell or ability that’s causing the creature to leave the battlefield is actually trying to exile it. In that case, the spell or ability succeeds at exiling the creature. If the spell or ability later returns the creature card to the battlefield (as Astral Drift might, for example), the creature card will return as a new object with no relation to its previous existence. The unearth effect will no longer apply to it.

So say you have an unearthed sliver and you activate the Frenetic ability of that sliver. If you win the coin flip, the ability will, in accordance with the above ruling, succeed in exiling and later returning the sliver.
If you lose the coin flip, the sliver will be sacrificed according to the Frenetic ability, and go to exile instead of your graveyard as Unearth dictates, without coming back later.


text:
What happens when one target of Paradoxical Outcome becomes illegal?
What happens when one target of Paradoxical Outcome becomes illegal and leaves the battlefield while Paradoxical Outcome is still on the stack? Does it fizzle?
The rules text of Paradoxical Outcome:

Return any number of target nonland, nontoken permanents you control to their owners’ hands. Draw a card for each card returned to your hand this way.

It would be helpful to include relevant card text into the question.  Links can decay or change.  Presumably the card could even change, which could potentially change a question like this.

On this site we operate under the assumption that Gatherer card links will be good indefinitely, and that card text will not change functionally. Gatherer is listed as the official source for card text in the Magic rules, and Magic cards get functional errata extremely rarely.

A spell only fizzles if all targets become invalid before resolution. The spell will resolve on the remaining targets, and a card drawn for each card actually returned to your hand.

608.2b If the spell or ability specifies targets, it checks whether the targets are still legal. A target that’s no longer in the zone it was in when it was targeted is illegal. Other changes to the game state may cause a target to no longer be legal; for example, its characteristics may have changed or an effect may have changed the text of the spell. If the source of an ability has left the zone it was in, its last known information is used during this process. If all its targets, for every instance of the word “target,” are now illegal, the spell or ability doesn’t resolve. It’s removed from the stack and, if it’s a spell, put into its owner’s graveyard. Otherwise, the spell or ability will resolve normally. Illegal targets, if any, won’t be affected by parts of a resolving spell’s effect for which they’re illegal. Other parts of the effect for which those targets are not illegal may still affect them. If the spell or ability creates any continuous effects that affect game rules (see rule 613.10), those effects don’t apply to illegal targets. If part of the effect requires information about an illegal target, it fails to determine any such information. Any part of the effect that requires that information won’t happen.

The last two sentences are particularly interesting. Does that mean that if there was a part of the effect that said "add an amount of {U} equal to their total converted mana cost", you would actually get no mana whatsoever if one of the targets become illegal?

@Fax I assume the wording would be more be similar like the existing wording specifying "for each card returned this way".  Then there's no problem since failing to return one of the targets won't change the CMC of those actually returned.

Paradoxical Outcome will not resolve (i.e. 'fizzle', though that term does not appear in the rulebooks) if you target only one permanent and that leaves the battlefield before it resolves. Otherwise, if there are any legal targets left, all of these will still be returned to their owners' hands and you'll draw some cards (one for each of those permanents you own).

608.2b If the spell or ability specifies targets, it checks whether the targets are still legal. A target that’s no longer in the zone it was in when it was targeted is illegal. Other changes to the game state may cause a target to no longer be legal; for example, its characteristics may have changed or an effect may have changed the text of the spell. If the source of an ability has left the zone it was in, its last known information is used during this process. If all its targets, for every instance of the word “target,” are now illegal, the spell or ability doesn’t resolve. It’s removed from the stack and, if it’s a spell, put into its owner’s graveyard. Otherwise, the spell or ability will resolve normally. Illegal targets, if any, won’t be affected by parts of a resolving spell’s effect for which they’re illegal. Other parts of the effect for which those targets are not illegal may still affect them. If the spell or ability creates any continuous effects that affect game rules (see rule 613.10), those effects don’t apply to illegal targets. If part of the effect requires information about an illegal target, it fails to determine any such information. Any part of the effect that requires that information won’t happen.

(emphasis mine)
The next step in spell resolution is

608.2c The controller of the spell or ability follows its instructions in the order written.

which will happen if it still has legal targets.

Although the word "fizzle" doesn't appear in the rules, it is simply a common shorthand for the bold sentence of 608.2b. So your first sentence is somewhat misleading (or at least ambiguous, it implies that fizzling isn't actually a rule, as opposed to the fact that the fizzle rule doesn't actually go by that name in the rules).


text:
Ugin's Conjurant vs. un-preventable damage
If I had Ugin's Conjurant with 10 +1/+1 counters on it (and no other effects modifying its toughness,) and my opponent cast a Banefire for 5 damage on it, would +1/+1 counters get removed from the Conjurant, as well as the damage being dealt, killing the Conjurant?
Relevant text on Banefire:

Banefire deals X damage to any target.
  If X is 5 or more, this spell can't be countered and the damage can't be prevented.

and on Ugin's Conjurant:

If damage would be dealt to Ugin's Conjurant while it has a +1/+1 counter on it, prevent that damage and remove that many +1/+1 counters from Ugin's Conjurant.

If Ugin's Conjurant takes damage that cannot be prevented, it will both take the damage and lose that many +1/+1 counters. This is covered by rule 615.12:

Some effects state that damage “can’t be prevented.” If unpreventable damage would be dealt, any applicable prevention effects are still applied to it. Those effects won’t prevent any damage, but any additional effects they have will take place. Existing damage prevention shields won’t be reduced by damage that can’t be prevented.

So, if the Ugin's Conjurant has 10 +1/+1 counters on it and it is hit with a Banefire for 5 damage, it will end up as a 5/5 with 5 damage marked and it will die.


text:
Temporary gain control effects, what happens if I give the permanent to another opponent before the effect ends?
Let's say that I temporarily gain control of an opponents permanent through some means, and then, before the temporary effect ends, I give it to another opponent (though let's say Harmless Offering). Will the permanent still return to the original opponent (presumably the owner), or will it stay under the control of the second opponent?
I can see this working differently in different scenarios, so let me give two examples:

Gaining control of a creature through Act of Treason which creates an effect that lasts until end of turn.
Gaining control of a creature through Control Magic, and then having Control Magic be destoryed after the creature has been given to the second opponent.

In both cases, the opponent you gave the permanent to will keep it.
When you take control of the permanent, you create a continuous control-changing effect that gives you control of the permanent. When you give the permanent to another player, you create another continuous control-changing effect that gives control of the permanent to that player. Once the first effect ends, either because the Act of Treason time runs out, or the Control Magic is destroyed, the second effect keeps working, so the opponent you gave the permanent to will still control it.

Change-of-control effects work a little like a stack, where the most recent one is on top and that's always the one currently in effect. What happens to the ones below is immaterial. Is how I think about it.


text:
Clarification on how the emblem gained by Tibalt, Cosmic Impostor works
I have two questions regarding the exact rulings of the emblem gained by Tibalt, Cosmic Impostor.
Question 1 The emblem gained by Tibalt mentions the card (Tibalt) by name. Looking at rule 201.4a stated below, am I correct in assuming that the emblem only grants you the ability to cast cards exiled with the specific Tibalt which created the emblem? Meaning that if, for example, Tibalt got bounced and was then replayed, and the new Tibalt's ETB got countered (resulting in no emblem being created), then any cards exiled with this new Tibalt would not be playable from exile (even though you still have the old emblem)?

201.4a If an ability’s effect grants another ability to an object, and that second ability refers to that first ability’s source by name, the name refers only to the specific object which is that first ability’s source. The second ability does not refer to any other object with the same name as the first ability’s source. However, if the second ability also moved the first ability’s source to a different public zone, the name refers to the object the source became in its new zone. This is also true if the second ability is copied onto a new object.

Question 2 What is the ruling for if some ability changed the name of Tibalt, for example if Tibalt was made into a copy of another permanent? Looking at rule 706.11, I assume that the emblem would track whatever permanent Tibalt became? And if this permanent has some ability which allows it to exile cards, am I correct in assuming that these cards would be playable from exile?

706.11 If an effect refers to a permanent by name, the effect still tracks that permanent even if it changes names or becomes a copy of something else.

Thanks for your time.

Normally I would have answered this question by quoting the rules that you included in the question. What are you looking for in an answer that isn't addressed by those rule quotations?

@murgatroid99 I was simply unsure about whether I had interpreted the rules correctly or not

@murgatroid99 it sounds like a misunderstanding of the difference between a triggered ability (when X happens, do Y) and a replacement effect (As X happens, do Y) Much of the issue becomes academic and moot once that's cleared up. There's no real way to have a tibalt without a matching emblem.

There absolutely are ways to have a Tibalt without a matching emblem, so the rest of the question is not moot.

@murgatroid99 How? There's no way to stop the replacement effect, nothing exists that can prevent emblems from being created, and modal DFCs cannot transform once in play.

Another permanent could become a copy of the Tibalt. Or it could be Manifested and then forcibly turned face up.

@murgatroid99 When turned face up from manifest, you have Valki, the front face, never Tibalt, the back face. I am trying to think of cards that can both target planeswalkers with copy effects and already be on the battlefield so as to not have the replacement effect happen while they enter as a copy of Tibalt. It might be doable but I am drawing a blank on how. Particularly since if it does happen, they would tend to die immediately from having no loyalty.

I actually forgot that Tibalt wasn't the front face. Gatherer doesn't communicate that clearly. And the copy effects don't have to target planeswalkers specifically. Tibalt can become another type and then be targeted by effects that apply to that type. For example, it could be made into an artifact and then targeted by Mizzium Transreliquat, or a creature and then be copied by Vesuvan Shapeshifter.

Let us continue this discussion in chat.

No and yes respectively to your questions.
For your first question, your analysis of rule 201.4a is correct, however you have an incorrect assumption in your question.  You assume that Tibalt's effect that creates the emblem can be countered separate of Tibalt, but it cannot.  Tibalt's effect is worded thus (emphasis mine):

As Tibalt enters the battlefield, you get an emblem with "You may play
cards exiled with Tibalt, Cosmic Impostor, and you may spend mana as
though it were mana of any color to cast those spells."

Since it is worded "As ..." it is a replacement effect, not a triggered ability.

614.1c Effects that read “[This permanent] enters the battlefield with . . . ,” “As [this permanent] enters the battlefield . . . ,” or
“[This permanent] enters the battlefield as . . . “ are replacement
effects.

A triggered ability would be worded as "When Tibalt enters the battlefield ..."

603.6a Enters-the-battlefield abilities trigger when a permanent enters the battlefield. These are written, “When [this object] enters
the battlefield, . . . “ or “Whenever a [type] enters the battlefield,
. . .” Each time an event puts one or more permanents onto the
battlefield, all permanents on the battlefield (including the
newcomers) are checked for any enters-the-battlefield triggers that
match the event.

Since it is written as a replacement effect, there is no ability that ever goes on the stack that can be countered to stop creating Tibalt's emblem separate from countering Tibalt himself!  So you could never get into a situation where 201.4a could apply (under normal casting circumstances, copying Tibalt or some other jankiness can cause it to happen).  If Tibalt hits the battlefield, so does his emblem.
For the second situation, your analysis of rule 706.11 is correct.  The game will track Tibalt and any cards exiled by it, no matter if it's name changes or not.

While it's true that Tibalt does not have a triggered ability, it is absolutely possible to have a Tibalt without having a corresponding emblem, so it is incorrect to say that 201.4a could never apply. For example, Tibalt could become an artifact or creature and then another permanent could become a copy of it. In addition 201.4a applies even in the simpler case where two separate Tibalts are played and you get both emblems.

@murgatroid99 That's fair, I'll clarify my answer to reflect that under normal casting circumstances it won't apply.  As with all things Magic, there's some way to make something janky happen.

Casting a second Tibalt after you previously controlled a Tibalt is an entirely normal circumstance in which rule 201.4a would apply.

@murgatroid99 True, but once you have one emblem per Tibalt the end result is the same that anything exiled by either Tibalt is tracked and able to be cast.  I'm not saying it never applies to Tibalt just that the number of situations where it makes a meaningful difference is fairly few,.  Especially in the scenario the OP was asking about it isn't (usually) relevant.

Yes to all - you found the relevant rules and interpreted them correctly.

Each specific Tibalt emblem will be tied to a specific Tibalt object, and there is no way to have a Tibalt walker without having an emblem also created. This is because the ability that creates the emblem isn't an ETB triggered ability, but a replacement effect, the word 'As' at the beginning of the ability marks it as a replacement effect, as explained in the Comprehensive Rules (emphasis mine):

614.1c Effects that read "[This permanent] enters the battlefield with...," "As [this permanent] enters the battlefield...," or "[This permanent] enters the battlefield as..." are replacement effects.

Replacement effects aren't separate from what they are replacing, you can't counter them without countering the event they replace - so when Tibalt enters the battlefield, the emblem enters at the same time.

Once the card is on the field, there is no way to transform from Valki into Tibalt. Not without returning it to hand and re-casting the Tibalt side as normal.
If Valki were in play and copied a creature that transforms in place (like Bloodline Keeper) nothing would happen (see 711.5). If Valki were to copy creature that exiles and transforms into a planeswalker (like Nicol Bolas, the Ravager) he would be exiled, but would not return (see 711.10a). These are because while they are all double-faced cards(DFCs), Modal DFCs and Transforming DFCs are covered by different parts of section 711 in the rules and handled in different ways (see 711.1).

711.5. Only permanents represented by transforming double-faced cards can transform. (See rule 701.28, “Transform.”) If a spell or ability instructs a player to transform any permanent that isn’t represented by a transforming double-faced card, nothing happens.

711.10a If a spell or ability puts a transforming double-faced card onto the battlefield “transformed,” it enters the battlefield with its back face up. If a player is instructed to put a card that isn’t a transforming double-faced card onto the battlefield transformed, that card stays in its current zone.

711.1 A double-faced card has a Magic card face on each side rather than a Magic card face on one side and a Magic card back on the other. There are two kinds of double-faced cards. Transforming double-faced cards include abilities on one or both of their faces that allow the card to “transform” (turn over to its other face) or allow the card to enter the battlefield “transformed” (with its back face up). Modal double-faced cards have two faces that are independent from one another and can’t transform.

Update: After a discussion on this question in chat with @Murgatroid99, there are ways to get a copy of Tibalt on the field without a matching emblem being created, though it seems all but one way (a clone like Vesuvan Shapeshifter that enters as one animated planeswalker (like Gideon Blackblade) to get loyalty without the emblem and still has the ability to change to something else later) will not have any loyalty counters, and die immediately, since placing starting loyalty counters on a planeswalker is also an enter the battlefield replacement effect.