On the question of En Passant Puzzles, the following comment is from
The British Chess Problem Society
What are Chess Problems?
I personally have seen en passant puzzles in newspapers, and some puzzle books. Usually the en passant allowance appear in more and most complicated positions.
En passant
An en passant capture can occur during the course of a solution following the normal rules of chess; that is, it has to be preceded by the appropriate double-step pawn move by the other side. In the diagram position an en passant capture is considered illegal unless it can be proved, by retrograde analysis, that the last move leading up to the diagram position was the appropriate double-step pawn move.