Checkmate by castling
White to move and checkmate in (2) moves:
There is no checkmate in 2 moves dum.bass.
There are some checkmates in 3 moves.
White to move and checkmate in (2) moves:
There is no checkmate in 2 moves dum.bass.
There are some checkmates in 3 moves.
1. o-o! (well, an assumption must be made, you can assume that the "o-o" checkbox for White is ticked for the puzzle)
You know what's next.

https://www.chess.com/analysis/game/live/10624086761
A rare example of castling with mate where moving the rook to that square (always legal if castling is legal) does not suffice.

It's not obvious to find the fastest mate. I improved it to blacks 7th move, so 10 clearly was not best
That made me laugh -- nice composition!
...Have any of you ever encountered checkmate/stalemate by castling, by en passant or some other unusual method before? I am rather curious. Share your thoughts in this thread.
Here is a famous en passant checkmate from a game in 1928.