Checkmate in -0.5 moves:
I bit my tongue on OP but can't do it twice. You don't retract the King first when you castle. Nor do you move the Rook first when playing forward.
*STOMP STOMP STOMP*
@shoopi - so it's as if white checkmated, then played another move right after?
Yes that's exactly right.
@roopi: Right, I remember that one now :)
It looks like -1.Nd5xRf6, but I don't see the purpose of all the pieces. Bb3 is promoted, sure - but that could have been Pf7 straight down. Not sure why it matters.
That's the correct solution. And the purpose of all the black pieces is to prevent the option of retracting f5xg6.
Oh, I see. f5xg6 would have been tricky to find because even though I'm breaking convention and leaving the enemy K in check with a retracted move, the convention is so engrained in my mind that I didn't even think about trying f5xg6.
1. Place the pawn on h8.
2. Remove the pawn from the board.
3. Don't promote it, hence only 2/3 of a move. Double stalemate.
This is an old one.
1) Finish castling
2) Lift the wK in the air.
Edit: hmm, but not sure 1) is valid because that would be 'white already playing' instead of 'white to play'. :P