Knightmare Chess is a proprietary game published by Steve Jackson Games.  It is something like a combination of chess and Magic: the Gathering.  In Knightmare Chess you play a regular game of chess, but in addition, you have a hand of cards that gives you "special powers".  This problem is inspired by that game.

Ooooops.  Misspelled "doppelganger" in the title.

Amy

White to move and mate in 1.

Your special power:  Doppelganger.  When you move, you may move one of your pieces like one of the enemy pieces in an adjacent square. 

Important clarification:  Your piece only moves like the enemy piece and only for one turn.  It does not retain that power, nor does it become the piece that it moves like.  For all other purposes it remains the original piece.  For example:  If you move a bishop as a knight, it still gives check as a bishop.  

Yeah, it's kind of complicated.  But I'm sure if you understand the rule, you'll solve the puzzle quickly.  Feel free to ask for clarification, and I will answer as soon as possible.

Assume that in reply to your move, your opponent can only make a standard chess move; i.e., he has no special powers available.

Pawn on d6 to e8=Ne8# with the power of the knight?

Right.  Very good !

I'm happy you understood my baroque rule explanation.

Amy

Also pawn c5-e5# (moving as rook), or pawn d6-e5# (moving as bishop).

Thanks. I hope you provide more of these types of puzzles, they are fun.

No these aren't correct because the special power only allows you to move your piece like an enemy piece that is located in an adjacent square.  There is no rook on the board, and the pawn on d6 is only adjacent to a friendly bishop.

The pawn on c5 could move as a bishop because it is adjacent to the black bishop.  It could move to d4, for example, but since it remains a pawn and not a bishop, it can't check from there.

Oops, missed that part. Thought it allowed you to move any piece like any other piece, for that move only.

lol wierd

First of all, the card you are thinking of is Hero Worship. Doppelganger allows pieces to move, for one turn, like the piece their opponent last moved. (For example, if black moves a rook, and white plays Doppelganger on white's turn, white can move any piece as if it were a rook).

Second of all, pawns moving with either Doppelganger or Hero Worship may not promote.

However, Hero Worship actually allows pieces to move like any piece in the 8 surrounding squares (either colour). Therefore, the actual solution to this is d6-e5# (moving like the white bishop).

Actually, I wasn't thinking of any particular card.  In fact, I didn't even know a Doppelganger card existed.  I just made up the power and the name.  Anything else was strictly a coincidence.