Find the decisive blow (difficulty 1560)

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Black to move

Show solution
12345678 hgfedcba
  1. c8–c7 key move
  2. c3–b5
  3. d6–b5

What makes it

The king strikes, a 5-point investment, and the attack wins. A piece slips off the line and the attack opens up behind it. It calculates 23 plies deep.