Originally posted by KneeCaps
Take back fxe8=R
[fen]4b1b1/5P1p/6kp/4K2p/6p1/6p1/1P1PP1P1/8 w - - 0 1[/fen]
and play fxg8=Q#
[fen]4b1Q1/7p/6kp/4K2p/6p1/6p1/1P1PP1P1/8 b - - 0 1[/fen]
I'm probably missing something. I never get any of your puzzles right.
Trouble is, this position is illegal!
Black's pawns captured 8 times. There are 6 white pieces on the board, and Bf1 and Bc1 died at home. That accounts for all 16 white pieces.
To promote a 2nd light square Bishop, Black would need to capture again ... but there is no capture available!