bondiggity wrote:
I'm pretty sure it's the queen. As RyanMK stated, hxg6, pawn to h7 seems to be the only way to get the pawn promoted, as the black bishop can't be sacrificed since it needs to be captured at a3.
The problem is how to get the Queen to g8. The queen can escape through the b7 hole and f6-g7-g8. This implies that the pawn structure must be fixed before promotion. This leaves us with the piece either being the white Queen or the white knight. Now the piece must be the queen since the only escape square for the Knight is f6, which would be check, ruining castling or the knight still being on the board. So white's promoted piece is the Queen.
Awsome! It took me quite some time to understand the sequence of captures. Well done!
I'm curious whether any of you have ever tried to compose a retrograde puzzle.
The closest I've come his this one that's basically a gimme even without the retrograde aspect especially since I called it "Mate in One":
http://www.chess.com/forum/view/more-puzzles/mate-in-one2