Hey, I got some chess variant ideas to experiment.
The first one is "en passant" chess : every slider (any piece but knight and king) can be taken en passant by any piece, pawn or king.
Capture en passant is defined as follow : a slider that makes a move without capture can be captured on any square lying on its path (initial and final square excluded, final square is obviously ok but not en passant). Like pawn capture en passant in regular chess, the capture has to be done right after the move (as a consequence there is at most one piece susceptible to en passant at anytime)
Since you cannot en passant capturing move, you cannot en passant en passant (en passant being a capture). The idea is that en passant captures the piece on its way preventing it to reach its destination, so a piece can't both successfully make a capture and be block on its way*, and priority is given to capture to prevent ill behaviour like perpetual en passant canceling each other.
*From a practical point of view, the fact that a piece can't both successfully make a capture and be captured en passant (not canceling the first capture) makes it possible to play with a standard chess plateform with takebacks.
One undesired exception is for move that block check, ideally, one should be able to take them en passant (exactly like pawns) but it's not possible to do with only takebacks, so let's say they can't be taken en passant.
Maybe we could use this thread to suggest other stupid variants.