Find the decisive blow (difficulty 1530)

12345678 hgfedcba

Black to move

Show solution
12345678 hgfedcba
  1. d5–g2 key move
  2. b2–a1
  3. f8–f1

What makes it

Mate is forced in 18. It is the queen that strikes first. 35 half-moves of forced play.