I had a rather odd idea today. On my own, I came up with a mate in two scheme that uses a fairy chess piece, along with a new puzzle theme. The idea is that you must figure what fairy piece is going to be used-changing a piece or by promotion-or is being used-intution based on the position and goals of the puzzle. Since this could get a bit broad, I'm limiting my usage to what can be found in the Wikipedia list of fairy chess pieces to narrow it down. I shall strive to make it not impossible to solve.
Thus, I present my original puzzle
Mate In 2, Black To Move:
EDIT: Gareth McCaughan has noticed a flaw, so here is a fix.
The Fix: The board is from White's POV. The 7th rank black pawns, and only those black pawns, may move up onto the 8th rank to promote. All of the other pieces move normally.
It is strange, but it is nessecary to get the idea behind the puzzle out. The pawns themselves are not the solution, although they would technically count as fairy pieces.
Identify the fairy piece that will be promoted. Give an explanation for your answer. You must also solve the mate in two-there is a total of four solutions possible.