Find the decisive blow (difficulty 1215)

87654321 abcdefgh

White to move

Show solution
87654321 abcdefgh
  1. g6–f7 key move
  2. f8–f7
  3. d1–d8

What makes it

The pawn sets up a forced mate in six. The forced line runs 11 plies. Rated 1215 — a fair workout.