Half move mates

Half move mates are puzzles of which you need to make half a move to solve. As a example,

the first half was the rook in castling, so the solution would be Kc1#

Another example:

the solution is  lifting your king in the air, as that is the first half of a move on a real life board!

Please post and create as many of these type of mates on this forum post as you can. Enjoy!

Here are a couple of mates in half moves I composed. I also have some mates in 0 moves, -0.5 moves, -1 moves and -1 moves for each side.

Mate in 0.5 moves:

I'm confused.

Tolosa showed this idea with 7 wK discoveries that spoil the mate.

Mate in half a move. Beware, it's a vicious one.
Answer in white : take the pawn g5 off the board, as half the 1.fxg5 en passant.

Remove the g5 pawn to capture it en passant. Well, that's the intended solution, but it's invalid because we did not prove black just played ...g7-g5.

I'm not sure there are really strict rules for half move mates.

I am.

http://www.saunalahti.fi/stniekat/pccc/codex.htm

lol why so serious?

I am on a mission to stamp out all frivolity. Although this forum makes my foot damn sore sometimes.

Wait, I thought the intended solution is to finish placing your Knight on h6, but the subsequent discussion makes me think that's not it.

Checkmate in -1 move. Basically white retracts a move resulting in a legal checkmate.

@shoopi - so it's as if white checkmated, then played another move right after?

I'm surprised no-one posted this yet, I've known this "halfmove mate" for decades:)

Yes that's exactly right.

@roopi: Right, I remember that one now :)

Checkmate in -0.5 moves:

Duh ! So you mean that...

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.

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*