Antichess is an eccentric variant where you lose all your pieces or get stalemated to win.

Rules

• 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.

Notes

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.