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12.f5 e5 and Black controls the center.
After 12.f5 e5 black has now an access on the d4-square. and have control the center. 12...Nd5!? is interesting with a complex game.
19...Nf5 s better. So if White take it 20.Bxf5 Rxd1+ 21.Nxd1 gxf5 then Black is better with an open position in compensation of the doubled pawns.
25...f5 is mistake, good job to spot it. Better is 25...f6 undermining the weak pawn on e5.
19. ... Nf5 20. Kg1 (threatening g4) h5 21. h3 h4 22. Rf1 and white is threatening to play Rf4 capturing the h-pawn, but first winning a pawn on f5. 22. ... Rd4 23. Bf5: Rd2 24. Be4 is not a good continuation for black and neither is 22. ... Rd4 23. Bf5: ef5: 24. Rf5: Rd2 25. Rf2. Therefor will black have to move its knight back to e7 and is the pawn on h4 vulnerable if not already lost.
I would suggest 19. ... Ng6, because it puts a structural threat capturing the isolated e-pawn. Defending with the rook is not pleasant, with the knight takes time to perform, with the bishop is impossible. Exchanging the knight with the bishop is good for black.
Hmm, 19. ... Nf5 20 Kg1 Bg2: 21. Kg2: Ne3+ 22. Kf3 Nd1: 23. Nd1: Rd5 24. Ke4.
Difficult choice what to play.
What about 19...Kh8 or 19...Kf8? Then I can find nothing better than 20.h3, getting the king activated.
I would prefer Kg1 to stop the pin on the g2-pawn immediately and moving the king to the centre. With the moves of the knight black activates his piece creating immediate threats. That does not happen with Kf8 (Kh8 is very passive, would not play it myself). The pawn on h7 is poisoned, but what does the combination of the knight on e7 and king on f8 do more then the knight on f5 or g6 and the king on g8? What do you see?
What about the hole on d5? And how will Black use d4?