Bughouse

Bughouse is played by four people in two teams on two boards at the same time. On each team, one player has White on one board and the partner has Black on the other. The games are connected by a rule that radically changes what a capture means.

When you capture an enemy piece, it does not simply leave the match. It goes into your partner's reserve. On a later turn, your partner may make a drop: instead of moving a piece already on the board, they place a reserve piece on an empty square. Under common rules, pawns cannot be dropped directly onto the first or eighth rank.

As a result, an event on one board can immediately change the possibilities on the other. A capture can supply exactly the piece a partner needs to attack, defend, or block a check. Team communication is therefore a normal part of Bughouse, and each board usually has its own clock.

Match-ending rules can vary by organizer or platform. On Chess.com, for example, the first loss, timeout, or resignation ends the match for both boards. The closest relative is Crazyhouse, but Crazyhouse has only two players and each player reuses the pieces they personally capture.