A simple task: It’s White to move selfmate themselves in three moves. White pawns are moving up.
The secret is that we are
allowing promotion to an enemy piece. A literal reading of a previous version of the promotion rule implied that promotion to an enemy piece was legal. See this question: https://chess.stackexchange.com/questions/2756/do-the-official-rules-of-chess-forbid-promoting-a-pawn-to-a-piece-of-the-opposit
As a result, we could
selfmate in two moves, as follows:
1. dxc8=bN+ Nd6 2. h8=bN Ng7#where the "b" prefix indicates that we are promoting to black knights in both cases.
However, the puzzle asks us to
selfmate in 3 moves instead. The only way to do so is to throw in an in-between move:
1. dxc8=bN+ Nd6 2. b8=bN+ Nc6 3. h8=bN Ng6#All moves are forced.
Here is an enigmatic answer.
1. b8=Q+ a natural first forcing move. 1. ... Rc6 only move.
2. Kg8!?&%@wtf$ The king tramples on the head of its own bishop. Because of course he can.
2. ... f6 only move.
3. Kh8 The bishop unfolds back to normal with squeaking noises.
3. ... f5# only move. And it's checkmate and you can't go back to g8 because, er... you can break the rules only once per game/when your opponent is not paying attention/when you're not in check/when your king is not on the h8 square.