user12: Although the Halloween Gambit is generally considered bad (and nearly losing for white), it is tricky to meet over the board, especially at the club level.
How should black play in order to refute white's gambit?
[White "Four Knights"]
[Black "Halloween Gambit"]
[FEN ""]

1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. Nxe5?! Nxe5 5. d4 Nc6 (5... Ng6)


user757: When meeting tricky (complex) positions, the best we can try is to simplify the position, this is for sure one of those tricky ones.
5...Nc6 seems like a good option
r1bqkb1r/pppp1ppp/5n2/4n3/3PP3/2N5/PPP2PPP/R1BQKB1R b KQkq d3 0 5

5... Nc6 6. e5 Ng8 7. Bc4 d6 8. Bf4 dxe5 9. dxe5 Bf5 10. O-O Qxd1 11. Raxd1 Bxc2 12. Rd2 


user307: Edit :
After posting this I realized that I just transposed to pretty common position, which I believe is not all that great for Black. But perhaps the idea of getting a crazy attacker to play a dry position is still valid, so I will keep my post up.
What about returning the knight right away with 5.d6. I don't think that white has any better moves than 6. dxe5 and then exchanging queens. Where white only has a slight advantage.
[FEN ""]

1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. Nxe5?! Nxe5 5. d4 d6 6. dxe5 dxe5 7. Qxd8 Kxd8

I realize that this is not everybody's cup of tea, and on pure chess level this is not impressive. However, this might be useful in practical sense. People who play Halloween Gambit love to attack; it is likely that the above resulting position is not to their taste. This would also take them out their opening territory.

user109: After 
[FEN ""]

1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. Nxe5?! Nxe5 5. d4 Nc6 6. d5

Instead of moving the c6 Knight, black should continue with Jan Pinski's 6...Bb4. Black will just give away the c6 knight and then black will take the e4 pawn with the f6 Knight.  White can't take the Knight because his own is pinned and if white moves their queen to d4, black can just move their queen to e7 to protect both the bishop and the knight.  A continuation might be something like this:
[FEN ""]

1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. Nxe5?! Nxe5 5. d4 Nc6 6. d5 Bb4 7. dxc6 Nxe4 8. Qd4 Qe7 9. Qxg7 Nxc3+ 10. Be3 Nd5+ 11. c3 Rf8

As you can see from above, if black plays accurately, there can be many discovered checks on white and if black wants, they can continue by taking the bishop on e3 eventually with another discovered check to follow or white will have to take the Knight, but either way, black will just take back with Qxe3+ and it is pretty much over for white.
Here is a professional game between Grigor Minchev and Aleksandr Pretov where black was unable to defend properly and was devastated.
  [FEN ""]
  1. e4 e5 2. Nf3 Nf6 3. Nc3 Nc6 4. Nxe5 Nxe5 5. d4 Nc6 6. d5
  Ne5 7. f4 Ng6 8. e5 Ng8 9. d6 cxd6 10. exd6 Qf6 11. Nb5 Rb8
  12. Be3 b6 13. Qe2 Kd8 14. O-O-O Qe6 15. f5 Qxf5 16. Qc4 Qe5
  17. Qc7+ Ke8 18. Bd4 Qf4+ 19. Kb1 Ra8 20. Re1+ Be7 21. g3 Qd2
  22. Bg2 Qxg2 23. dxe7 N8xe7 24. Nd6+ Kf8 25. Qd8# 1-0


12: <p>Although the Halloween Gambit is generally considered bad (and nearly losing for white), it is tricky to meet over the board, especially at the club level.</p>

<p>How should black play in order to refute white's gambit?</p>

<pre><code>[White "Four Knights"]
[Black "Halloween Gambit"]
[FEN ""]

1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. Nxe5?! Nxe5 5. d4 Nc6 (5... Ng6)
</code></pre>
 757: <p>When meeting tricky (complex) positions, the best we can try is to simplify the position, this is for sure one of those tricky ones.</p>

<p><code>5...Nc6</code> seems like a good option</p>

<pre><code>r1bqkb1r/pppp1ppp/5n2/4n3/3PP3/2N5/PPP2PPP/R1BQKB1R b KQkq d3 0 5

5... Nc6 6. e5 Ng8 7. Bc4 d6 8. Bf4 dxe5 9. dxe5 Bf5 10. O-O Qxd1 11. Raxd1 Bxc2 12. Rd2 
</code></pre>
 307: <p><strong>Edit :</strong></p>

<p>After posting this I realized that I just transposed to pretty common position, which I believe is not all that great for Black. But perhaps the idea of getting a crazy attacker to play a dry position is still valid, so I will keep my post up.</p>

<p>What about returning the knight right away with <code>5.d6</code>. I don't think that white has any better moves than <code>6. dxe5</code> and then exchanging queens. Where white only has a slight advantage.</p>

<pre><code>[FEN ""]

1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. Nxe5?! Nxe5 5. d4 d6 6. dxe5 dxe5 7. Qxd8 Kxd8
</code></pre>

<p>I realize that this is not everybody's cup of tea, and on pure chess level this is not impressive. However, this might be useful in practical sense. People who play Halloween Gambit love to attack; it is likely that the above resulting position is not to their taste. This would also take them out their opening territory.</p>
 109: <p>After </p>

<pre><code>[FEN ""]

1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. Nxe5?! Nxe5 5. d4 Nc6 6. d5
</code></pre>

<p>Instead of moving the <code>c6 Knight</code>, black should continue with <a href="http://en.wikipedia.org/wiki/Four_Knights_Game,_Halloween_Gambit#Pinski.27s_6...Bb4">Jan Pinski's <code>6...Bb4</code></a>. Black will just give away the <code>c6 knight</code> and then black will take the <code>e4 pawn</code> with the <code>f6 Knight</code>.  White can't take the Knight because his own is pinned and if white moves their queen to <code>d4</code>, black can just move their queen to <code>e7</code> to protect both the bishop and the knight.  A continuation might be something like this:</p>

<pre><code>[FEN ""]

1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. Nxe5?! Nxe5 5. d4 Nc6 6. d5 Bb4 7. dxc6 Nxe4 8. Qd4 Qe7 9. Qxg7 Nxc3+ 10. Be3 Nd5+ 11. c3 Rf8
</code></pre>

<p>As you can see from above, if black plays accurately, there can be many discovered checks on white and if black wants, they can continue by taking the bishop on <code>e3</code> eventually with another discovered check to follow or white will have to take the Knight, but either way, black will just take back with <code>Qxe3+</code> and it is pretty much over for white.</p>

<p>Here is a professional game between <code>Grigor Minchev</code> and <code>Aleksandr Pretov</code> where black was unable to defend properly and was devastated.</p>

<pre><code>  [FEN ""]
  1. e4 e5 2. Nf3 Nf6 3. Nc3 Nc6 4. Nxe5 Nxe5 5. d4 Nc6 6. d5
  Ne5 7. f4 Ng6 8. e5 Ng8 9. d6 cxd6 10. exd6 Qf6 11. Nb5 Rb8
  12. Be3 b6 13. Qe2 Kd8 14. O-O-O Qe6 15. f5 Qxf5 16. Qc4 Qe5
  17. Qc7+ Ke8 18. Bd4 Qf4+ 19. Kb1 Ra8 20. Re1+ Be7 21. g3 Qd2
  22. Bg2 Qxg2 23. dxe7 N8xe7 24. Nd6+ Kf8 25. Qd8# 1-0
</code></pre>
