morea: This puzzle has many acceptable solutions, all with the central theme of capturing on e6 with the Knight.First I didn't think 25. Qxf4 was good, because Black can mirror White's moves: 25. Qxf4 Qxc5 26. Rxc5 Rxf4, and the position is equal. So instead, I preferred the simple 25. Nxe6+ Nxe6 26. Rxc7+ Nxc7 27. Qa5, which wins a Queen and Pawn for Rook and Knight, with additional threats.
Then I realized that after 25. Qxf4 Qxc5 White can continue taking pieces like 25...Qxc5 26. Qxf5 Qxc3 27. Qxf8+! (this can't be copied!) Kxf8 28. bxc3 and White emerges a Rook ahead. So instead, after 25. Qxf4! Black is better off continuing with 25...Qd6 26. Qd2, losing only the Knight, which is better for White than the previous line.
Then looking further into 25. Nxe6+, we have 25... Nxe6 26. Rxc7+ Nxc7 27. Qb4! (with the threat Qe7+ winning at least another exchange) Bf7 28. Nxf7 R5xf7 29. Qxb7, which wins Queen and two Pawns for Rook and Knight, so about just as good.
Then, of course, we can also just dislodge the Knight protecting e6: 25. g3
Qe7 (else the Queen falls) 26. gxf4 Rxf4 wins a Knight for a Pawn.
I think even this works: 25. g4 Rxe5 (on Rf6 26. Knight takes on e6 as always) 26. Nxe6+ Nxe6 27. Rxc7+ Nxc7 28. Rxe5 and White is comfortably better.
Or we could just attack e6 with one more piece before taking on it: 25. Ned3 Bf7 26. g4 Rf6 27. Nxe6+ Nxe6 28. Rxc7 Nxc7 29. Qxg5+ winning.
Or just win the exchange with 25. Ncd7 Qd6 26. Nxf8 Rxf8.
In conclusion, 25. Qxf4, Nxe6+, g3, g4 and Ned3 are all good. Ncd7 is not as strong, but still winning.
In contrast, playing 25. Re4 would be a very bad idea. So at least some moves are not good...