Lose all your pieces (or get stalemated) to win the game.
Antichess is an eccentric variant where you lose all your pieces or get stalemated to win.
Pieces move the same way they do in standard chess; however, kings lose their royal powers - they cannot castle, and checks are no longer a threat. Since kings have lost their royal powers, pawns may be promoted to kings.
Capturing is forced. If you can take a piece, you must. If multiple pieces can be captured, you may choose which piece you capture.
To compensate for the nature of Antichess, you will always be given a chance to decide for promotions, even if you have enabled the option to always promote to Queens.