2024/06/04 DPA: "Little Jack Horner Sat In A Corner..."

Black to move.

White's King has limited mobility.

I've seen this pattern before:  Black would like to checkmate with his Knight on g3 and Rook on h1.  But if Black plays the setup move 1. ... Ng3, White escapes with 2. Kf2.

[Edit:  Stockfish doesn't even bother "escaping" since the King on g1 rather than h2 means Black cannot checkmate anymore.]

Also, note that White has no threats or even any checks so Black does have time for a setup move.

Black must not assume White will err with 2. Rc1, protecting the back rank, which allows 2. ... Ne2+, forking the King and Rook.  But after 3. Kf2 Nxc1, White has enough material to draw due to the passed pawn and Bishop pair.

1. ... Ra1+ [get to the back rank before White can defend it; it also X-Ray defends the Knight so it cannot be captured]  2. Kh2 Ng3 and nothing can stop ... Rh1# [White can insert 3. Rc1 and 4. Be1 but they only delay the inevitable].

.

The key was recognizing the need to reach the back rank before White could defend, force the King to h2, and realize that Black's Knight was X-Ray defended after 1. ... Ra1+.