An en passant pawn move is a legal move and played in chess tournaments and chess matches worldwide.
How many Times can you En Passant?
Eight times. Every pawn can capture en passant only one time. This happens when the opponent’s pawn advances two squares from its original square and is sitting right beside your pawn.
Can you En Passant a Queen?
Of course not, only a pawn can capture en passant.
Is En Passant useful?
This depends on the position. If you can capture en passant then think for a while and if it is useful you capture the pawn en passant and if not useful then you don’t do it. Simple.
What’s the Point of En Passant?
There is no point, it’s a rule, nothing else. If you want to learn chess then you have to accept it.
White can advance his e-pawn to e4.
Black may capture En Passant. He doesn’t have to, it is up to him.