Bughouse chess - Wikipedia

It seems to me that the rules can vary from place to place.  For example, it was common to now allow a dropped piece to deliver checkmate.

"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. (A variant does not allow dropped pieces to deliver check.) Dropped pawns may promote, but all promoted pawns convert back to pawns when captured. In play over the board, a promoted pawn can be put on its side to indicate promotion.[5] A pawn placed on the second rank may move two squares on its first move. A rook placed on the rook's typical starting square (a1, h1, a8, h8) may take part in castling. Each player must keep the reserve or stock pieces on the table in front of the board, always visible to all players of the game."

I don't like Bughouse much, but it can be a fun diversion...

Controversy[edit]

Bughouse chess is controversial among chess teachers. While some instructors find beneficial learning outcomes for bughouse, most do not consider it to have a positive effect, especially for novice chess players.^[54] According to Susan Polgar, "If your children want to play bughouse for fun, it is OK. But just remember that it is not chess and it has no positive value for chess. In fact, I absolutely recommend no bughouse during a tournament."^[55] Arguments supporting a negative view of bughouse include that it distorts typical chess pattern recognition^[56] and that it too heavily emphasizes tactical play at the expense of positional strategy.^[57] For example, in bughouse, one can just drop a pawn to compensate for a weakness created by moving one, unlike normal chess. It also lacks endgame play due to pieces being recycled, thereby reducing the need for precise moves. In addition, the lack of control over teammates' boards introduces randomness that is not encountered in normal chess. Further, many claim that since there is no set order of moves between the two boards, normal calculation ability is diminished. It also shares criticisms with speed chess in general, potentially encouraging a habit of moving too fast or playing unsoundly with the expectation that one's opponent will be moving quickly.^[36]

https://en.wikipedia.org/wiki/Bughouse_chess