Knight endgames can be very tricky, especially when there are passed pawns involved.
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[Event "rated untimed match"]
[Site "?"]
[Date "1952.??.??"]
[Round "?"]
[White "Kotov"]
[Black "Stoltz"]
[Result "0-1"]
[Annotator "David Hayes"]
[BlackElo "0"]
[FEN "6r1/Qp5k/8/3p3p/5q2/1P3p1B/P6P/5N1K b - - 0 1"]
[SetUp "1"]
[TimeControl "0"]
[WhiteElo "0"]
1... f2 2. Bg2 Qf3 3. Qxb7+ Kh8 4. Ng3 ( { White can try: } 4. Qxd5 Qxd5 5. Ng3 f1=Q+ 6. Nxf1 Qxg2# ) 4... f1=Q+ 5. Nxf1 Qxg2# 0-1