Bughouse (or doubles chess) is a variant of chess played by four players in teams (partnerships) of two on two separate chessboards. Each partner plays an opposing team member with the goal being to win the game by normal means (checkmate or timeout). One partner plays Black, the other White. Partners help each other by capturing enemy pieces which their partner may then place (drop) on an empty square on their turn.
Base Rules
When you capture one of your opponent's pieces, it is immediately passed to your teammate's "piece bank" for him or her to use at their discretion.
On any turn, instead of making a move, a player can "drop" any piece from their "bank" to any open square on the board.
Pawns can not be dropped on the 1st or 8th ranks.
A pawn that is placed on the 2nd rank may move two squares on its first move, as in standard chess.
Pawns that have promoted and are then captured go into the "bank" as pawns, not as the piece to which they promoted. Such promoted pieces are called "counterfeits."
A bughouse game is over when a game on either board ends in checkmate, resignation, or timeout.
When you capture one of your opponent's pieces, it is immediately passed to your teammate's "piece bank" for him or her to use at their discretion.
For example, whenever White captures a piece on Board A - it would be passed to their right where their partner's piece bank is located.
On any turn, instead of making a move, a player can "drop" any piece from their "bank" to any open square on the board.
There is an exception that applies to pawn dropping.
Pawns can not be dropped on the 1st or 8th ranks.
In addition to pawn dropping, there are additional rules that apply to pawns.
A dropped pawn that is placed on the 2nd rank may move two squares on its first move, as in standard chess.
A pawn can be promoted to any piece when it reaches the 1st or 8th ranks.
Pawns that have promoted and are then captured go into the "piece bank" as pawns (not as the piece to which they promoted).
Such promoted pieces are called "counterfeits."
A bughouse game is over when a game on either board ends in checkmate, resignation, or timeout.
https://upload.wikimedia.org/wikipedia/commons/c/c9/Bughouse_game_animation.gif
https://www.chess.com/article/view/bughouse-chess-tips-for-beginners
https://www.czechopen.net/en/festival-tournaments/l-bughouse/rules/
https://chat.openai.com/c/d67c3262-8957-4327-84ef-f973092bfe33