Here’s an odd challenge: What is the fastest way for an en passant checkmate after all other seven en passant captures have been done?
Here's one try:
[FEN ""] 1.d4 b5 2.d5 c5 3.dxc6 b4 4.a4 bxa3 5.b4 d5 6.b5 a5 7.bxa6 d4 8.c4 dxc3 9.h4 f5 10.h5 g5 11.hxg6 f4 12.e4 fxe3 13.g4 Bb7 14.g5 h5 15.gxh6 e5 16.Ke2 e4 17.Qe1 Bc5 18.Nh3 Bxc6 19.f4 exf3#
While this probably isn't the fastest possible, it can't get much faster. There are 8 en passants possible, and each takes 4 half moves to set up and execute (advance to 4th rank, advance to 5th rank, opponent moves pawn, capture pawn.) Those 32 half moves takes you through move 16, and you obviously need other moves somewhere to make it be a checkmate.