I had an odd idea. I made a mate in two that uses a fairy chess piece. However, the twist is that you must figure what fairy piece is going to be used (changing a piece or by promotion) or is being used based on the position and stipulation.
Mate In 2, Black To Move
Black’s 7th rank pawns move upward (Thanks for the help @Gareth McCaughan!)
Identify the fairy piece that will be promoted, and state why. You must also solve the mate in two.