Find the decisive blow (difficulty 1035)

12345678 hgfedcba

Black to move

Show solution
12345678 hgfedcba
  1. c8–h3 key move
  2. g2–g1
  3. e5–a1

What makes it

It starts with a bishop move and forces mate in four. 7 half-moves of forced play. Difficulty 1035: a solid test.