Dealing with Sénéchaud Countergambit in King’s Gambit How would you try to refute the Sénéchaud Countergambit in King's Gambit? 

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1.e4 e5 2.f4 Bc5 3.Nf3 g5
Full disclosure: I don't play the King's Gambit.  My first thought (and note that I am NOT a master-level player) was 4. Nxg5 exf4 5. Nf3 (which, in and of itself, isn't sufficient to be an answer).

I decided to just do some Googling to try to learn more about this, and stumbled across analysis.cpuchess.com, which allowed a position to be analysed by various chess engines.

Here's what they gave me:

Houdini


  
  Nxg5 h6 5. Qh5 Qf6 6. Nf3 Qxf4 7. Qxe5+ Qxe5 8. Nxe5 d6 9. Nf3 Nc6 10. b3 Nge7 11. Bb2 Rg8 12. d4 Bb4+ 13. c3 Ba5 14. Nbd2 b5 15. g4 Bxg4 16. Bxb5 O-O-O
  


GarboChess JS


  
  Nxg5 Qe7 5. Bc4 exf4 6. Qh5 Nf6 7. Qxf7+ Qxf7 8. Bxf7+ Ke7 9. e5 Ng4
  


Fruit

Seemed to be locking up mid-analysis.

Stockfish


  
  Nxg5 Nc6 5. Qh5 Qf6 6. Bc4 Nh6 7. Nc3 Qg6 8. Qxg6 hxg6 9. Nd5 Bb6 10. Bb3 d6 11. d3 f5 12. Rf1 Bd7 13. fxe5 dxe5 14. exf5 Nxf5
  


Toga2


  
  Nxg5 Qe7 5. Nc3 exf4 6. Nf3 Bb4 7. e5 Bxc3 8. dxc3 d6 9. Qd5 Nc6 10. Bxf4 Nf6
  


Critter


  
  Nxg5 exf4 5. Qh5 Qe7 6. Bc4 Nf6 7. Qxf7+ Qxf7 8. Bxf7+ Ke7 9. Bb3 h6 10. Nf3 Nxe4 11. d4 Bd6 12. O-O Re8 13. Ne5 Nc6 14. Rxf4 Ng5 15. h4 Nxe5 16. hxg5
  


Observation

What I found most amusing about this was that all of them (except Fruit, of course) suggested 4. Nxg5 as the best move... but that most went different directions afterwards; 4. ... Qe7 on GarboChess JS and Toga2 being the only commonality, and even they diverged almost immediately.

... which leads me to conclude that the answer to "how would you try to refute" is 4. Nxg5 followed by "tactics."