Find the decisive blow (difficulty 1530)

12345678 hgfedcba

Black to move

Show solution
12345678 hgfedcba
  1. g5–g1 key move
  2. f1–e2
  3. h1–e4

What makes it

It starts with a rook move and forces mate in 19. It calculates 37 plies deep. Difficulty 1530: punishing to calculate.