Originally posted by SwissGambit
Assiac [Heinrich Fraenkel]
Adventures in Chess 1951
[fen]2b5/Bk1p4/pP6/2P5/7p/6bK/8/5B2 w - - 0 1[/fen]
White to play. Who gets mated?

Under the old rules, White would have mate by 1.Bg2#. With the new two-step initial move, the result is reversed - Black replies 1...d5#, and the ep rule is of no help to white.

Originally posted by Essex 3
However after 1. Bg2+ d5 : -
White still wins as he can play 2. Bxd5#

Apologies. I overlooked the Prelate skulking on c8.

I think whomever taught you was derelict in not teaching you such an important move. Another thing you should be aware of is that it can only be done immediately following you opponent's move and only when opponent's move is pawn in question's first move and a two rank move, never on a one rank move. I had someone try capturing me en passant when it was not a two rank move. No en passant since his pawn was not passed.