Crazyhouse is a chess variant very similar to bughouse chess, but with only two players. It effectively incorporates a rule in shogi (Japanese chess), in which a player can introduce a captured piece back to the board as his own. * A captured piece reverses color (useful to have 2 sets on hand for this variant) and goes to the capturing player's 'reserve', or 'pocket'. At any time, instead of making a move with a piece on a board, a player can 'drop' a piece, in his reserve, onto an empty square on the board. * Promoted but captured pawns are dropped as pawns. * Pawns must not be dropped on the 1st or 8th ranks. * Drops which cause immediate checkmate are allowed. Unlike in shogi, this includes pawn drops. * A check that would cause checkmate, in regular chess, can be answered if the defender can make a legal drop which blocks the check.