1. e2e4  1... e7e5  2. g1f3  2... b8c6  3. f1b5  3... g8f6  4. d2d3  4... f8c5  5. b5c6  5... d7c6  6. b1d2  6... f6d7  7. e1g1  7... e8g8  8. d2c4  8... f8e8  9. g1h1 [%c_effect h1;square;h1;type;Interesting;persistent;true] Not a very popular move, but it was played in two important games in 2022 by Ukrainian GM Kirill Shevchenko. GMs Viswanathan Anand and Fabiano Caruana, among others, have also tried this move in older games. The main idea of the mystery king move is to prepare the f-pawn advance and also vacate the g1-square for the white knight, which can maneuver via g1-e2-g3, as will happen in the game. Of course, it's hard to believe that this plan gives White an objective advantage, but what is sought in this line is a middlegame position that allows for the creation of imbalance. 9... b7b6 A theoretical novelty. The move is natural, as the pawn on b6 is useful to reinforce the structure after the c6-c5 move, something that will inevitably happen sooner or later. Furthermore, the bishop can be developed on b7 in some cases. 10. f3g1 Kosteniuk sticks to the expected plan. 10... d7f8 Continuing the dance with the knights. 11. g1e2  11... f8g6  12. e2g3 White gives up the f4 break. 12... c8e6  13. c4e3  13... f7f6  14. g3f5 This move is the beginning of White's problems, as it won't be easy to execute a promising plan after this. It seems correct to take the other knight to f5: in that case, White could transfer the queen to g4 and then play h4-h5. It's always nice when we know what our next moves will be in an ideal world. 14... d8d7  15. d1f3  15... g8h8  16. f1g1 Kosteniuk clearly wants to advance the g-pawn. 16... g6f4 [%c_effect f4;square;f4;type;GreatFind;persistent;true] 17. g2g3 [%c_effect g3;square;g3;type;Inaccuracy;persistent;true] Now White's position is worse. 17... f4h3  18. g1f1  18... h3g5  19. f3e2  19... g5f7 The knight now defends the king and can still maneuver up to d4. Also, now the way is clear to play g6 and drive out the white knight. It's worth remembering that, without the light-squared bishop, White can have serious problems if the position opens up since his king won't be safe. 20. b2b3  20... f7d6  21. f5h4  21... d6b5 This knight is a real worker $1 22. c1b2  22... c5d4 [%c_effect d4;square;d4;type;GreatFind;persistent;true] It's useful to exchange the bishop so the pawn can move to c5. 23. b2d4  23... b5d4  24. e2d1  24... c6c5  25. c2c3 [%c_effect c3;square;c3;type;Inaccuracy;persistent;true] Removing the knight from d4 is very costly, as the pawns are weakened. 25... d4c6  26. d1e2  26... a7a5 [%c_effect a5;square;a5;type;GreatFind;persistent;true] Black has a comfortable advantage, thanks to the better pawn structure. 27. f2f4  27... a5a4  28. a1b1  28... a4b3  29. a2b3  29... e8d8  30. f1d1  30... a8a3  31. e2c2  31... b6b5 [%c_effect b5;square;b5;type;Interesting;persistent;true] Preparing Qf7 without White being able to put the knight on c4. Furthermore, a plan with b5-b4 is also possible. 32. h4f3  32... d7f7  33. f3d2  33... e5f4  34. g3f4  34... f6f5 [%c_effect f5;square;f5;type;Mistake;persistent;true] From now on Black starts to lose the advantage. 35. e4f5 