user9192: Jonathan Scrantz played this game against Lichess Level 8:
[Title "Jonathan Scrantz VS Stockfish Level 8 (3000) after 9. Kh1"]
[FEN ""]
[Startply "17"]

1. e4 e5 2. Bc4 Bc5 3. b4 Bxb4 4. f4 exf4 5. Nf3 Be7 6. d4 Bh4+ 7. g3 fxg3 8. O-O gxh2+ 9. Kh1 d5 10. exd5 Bh3 11. Nc3 Bxf1 12. Qxf1 Bf6 13. Ba3 Ne7 14. Ne4 O-O 15. Nxf6+ gxf6 16. Bxe7 Qxe7 17. Bd3 Qd7 18. Qg2+ Kh8 19. Bxh7 Qxd5 20. Qh3 Kg7 21. c4 Qa5 22. Qg2+ Kh6 23. c5 Rh8 24. Nh4 Qxc5 25. dxc5 Kh5 26. Nf5 Rxh7 27. Rf1 Rg7 28. Qxg7 Na6 29. Rf3 b6 30. Rh3#

I am aware that Lichess Level 8 deliberately makes mistakes, but I wonder whether it really did so in this game or not. It seems to me that 12. ... Bf6 was the definitively losing move. But SF10+ on that position at depth 24+ thinks that Bf6 has score +1.9 compared to +1.3 for Be7, so did Black already have a losing position before move 12? If so, where is the first point at which Black made a clear mistake and what is the general (human) strategy for White to win from that point?

user24098: Black had a losing position after 7...fxg3. The best way for black to go for a draw at this point was to play 7...d5, which continues 8.Bxd5 fxg3 9.O-O Nf6 10.Ba3 gxh2+ 11.Kh1 Nxd5 12.exd5 Qxd5 13.Nc3 Qa5 +=.
There are two possible continuations for black after 8.O-O, which are 8...d4 and 8...gxh2+, that may not seem initially bad, but are completely losing. I've detailed those in the following study: https://lichess.org/study/URz9uXJd
Please ask me any further questions if your confused.

9192: <p>Jonathan Scrantz <a href="https://www.youtube.com/watch?v=P8hkXKHWnhw" rel="nofollow noreferrer">played this game against Lichess Level 8</a>:</p>
<pre><code>[Title &quot;Jonathan Scrantz VS Stockfish Level 8 (3000) after 9. Kh1&quot;]
[FEN &quot;&quot;]
[Startply &quot;17&quot;]

1. e4 e5 2. Bc4 Bc5 3. b4 Bxb4 4. f4 exf4 5. Nf3 Be7 6. d4 Bh4+ 7. g3 fxg3 8. O-O gxh2+ 9. Kh1 d5 10. exd5 Bh3 11. Nc3 Bxf1 12. Qxf1 Bf6 13. Ba3 Ne7 14. Ne4 O-O 15. Nxf6+ gxf6 16. Bxe7 Qxe7 17. Bd3 Qd7 18. Qg2+ Kh8 19. Bxh7 Qxd5 20. Qh3 Kg7 21. c4 Qa5 22. Qg2+ Kh6 23. c5 Rh8 24. Nh4 Qxc5 25. dxc5 Kh5 26. Nf5 Rxh7 27. Rf1 Rg7 28. Qxg7 Na6 29. Rf3 b6 30. Rh3#
</code></pre>
<p>I am aware that Lichess Level 8 <a href="https://chess.stackexchange.com/a/35317">deliberately makes mistakes</a>, but I wonder whether it really did so in this game or not. It seems to me that <code>12. ... Bf6</code> was the definitively losing move. But <a href="https://lichess.org/analysis/fromPosition/rn1qk1nr/ppp2ppp/8/3P4/2BP3b/2N2N2/P1P4p/R1B2Q1K%20b%20kq%20-%200%2012" rel="nofollow noreferrer">SF10+ on that position</a> at depth 24+ thinks that <code>Bf6</code> has score <code>+1.9</code> compared to <code>+1.3</code> for <code>Be7</code>, so did Black already have a losing position before move 12? If so, where is the first point at which Black made a clear mistake and what is the general (human) strategy for White to win from that point?</p>
 24098: <p>Black had a losing position after 7...fxg3. The best way for black to go for a draw at this point was to play 7...d5, which continues 8.Bxd5 fxg3 9.O-O Nf6 10.Ba3 gxh2+ 11.Kh1 Nxd5 12.exd5 Qxd5 13.Nc3 Qa5 +=.</p>
<p>There are two possible continuations for black after 8.O-O, which are 8...d4 and 8...gxh2+, that may not seem initially bad, but are completely losing. I've detailed those in the following study: <a href="https://lichess.org/study/URz9uXJd" rel="nofollow noreferrer">https://lichess.org/study/URz9uXJd</a></p>
<p>Please ask me any further questions if your confused.</p>
