Go ahead, what is the shortest checkmate you can find delivered with an en-passant move?
Or have an educated guess how much moves it takes?
The best I can come up is 7 moves, I don't have a direct proof you can't make it in 6, but it seems unlikely you can make a "cage" for your king in less moves than that.
1. f3 h5 2. Kf2 Nh6 3. d3 d5 4. h3 Bxh3 5. Be3 Nf5 6. Qe1 h4 7. g4 hxg4 e.p. #
Here is my attempt, a mate in 6:
@ubdip, oh I did not see the mate in 6 first, nice one :)
Actually I found the one in #3 myself, too. Exactly the same! :D
(I have another ace up my sleeve!)
6 moves, different from #3
I have one in 6 moves as well. I think its a little more aesthetic (unbiased opinion :) ) since it is not at the edge of the board and none of the black pieces are en prise during the game.
#4 @NemPlayer Wow, never thought such a double check is even possible. That we can use for check two pieces that don't actually move!
I found a 7-move mate for white with more orthodox double checkmate. lichess.org/Zw38s2MS
I quite convinced myself it is not possible to deliver a checkmate en passant to the player who only made 5 moves, albeit I don't have a formal proof of this.
#9, ok. 5.5 moves not possible? (White 6. ep#)?