Bughouse

Bughouse is a chess variant played on two chessboards by four players in teams of two. Each team member faces one opponent of the other team. One player per team has black pieces, while the other has white pieces. Each player plays the opponent as in a standard chess game, with the exception of the rules specified below.

Rules

Shortened version of https://en.wikipedia.org/wiki/Bughouse_chess CC BY-SA 4.0

Captured pieces

A player capturing a piece immediately passes that piece to their partner. The partner keeps these pieces in their reserve and may, on their turn, instead of playing a regular move, place one of these pieces on the board (as in shogi and crazyhouse), called dropping the piece. Pieces in reserve may be dropped on any vacant square, including squares where the piece delivers check or checkmate; however, pawns may not be dropped on the first or last rank. Dropped pawns may promote, but all promoted pawns convert back to pawns when captured. A pawn placed on the second rank may move two squares on its first move, and, if it lands directly next to an enemy pawn, be captured en passant.

End of the game

The match ends when the game on either board ends. A game is won when one player gets checkmated, resigns or runs out of time.

Communication

Partners are normally allowed to talk to each other during the game. They can, for instance, ask for a specific piece, for more trades, ask to hold a piece, suggest moves or ask their partner to stall. Shouts like "Knight mates!" or "Don't give up a Bishop!" are common and can lead to seemingly absurd sacrificial captures on the other board. Partners are not allowed to physically act on the other board.