Keys "s"=save "l"=load "b"=back once
Ralph Betza, 1977. This is one of the most popular chess variants. After each legal move, advance one of your opponent's pawns one square if you can do so. (Exception: White does not advance a red pawn on the first move.) If you are forced to check yourself by advancing a pawn, you lose. This takes precedence even if you just checkmated your opponent. There is no en passant capturing. I had enemy pawns advanced to promotion be amazons.
These are simple illustrations rather than strong opponents.
Bug reports? -- Thank you! Keep them coming!