Originally posted by David113
[fen]7N/Ppp2P2/Rrk4P/K1P5/1P2P2P/2P4Q/5p1R/5NB1 w - - 0 1[/fen]
Selfmate in 3 moves.
If I were a betting man, I'd bet on a Babson.
1.a8B pins the b7 pawn. White's plan is to allow fg1, then kill the promoted piece. Black then has nothing left but ...Rxa6#.
1...fxg1Q 2.f8Q Qxc5+ 3.b5+! Qxb5# [Qf8 needed to control g8 and d6]
1...fxg1R 2.f8R! Rxf1 3.Rxf1 Rxa6# [a wQ on f1 spoils the mate]
1...fxg1B 2.f8B! Bxc5 3.Bxc5 Rxa6# [Qc5 checks prematurely]
1...fxg1N 2.f8N! Nxh3 3.Rxh3 Rxa6# [Nf8 needed to guard d7]
I have given only the lines that show the reasoning behind White's promotions.