Touch-move rule move or capture the first of the pieces that they touched. If it cannot be determined whether he touched his own piece or the opponent's piece first, it is assumed that he touched his own piece first. If a player touches more than one piece, he must move or capture the first piece that can be legally moved or captured. An exception to that is an attempted illegal castling; in that case the king must be moved if possible, but otherwise there is no requirement to move the rook. When castling, the king must be the first piece touched. If
Pocket Mutation Chess chess. Instead of moving, a player can take one of their own pieces from the board and put it into the pocket, provided that the pocket is empty. If the piece is placed into the pocket from the last rank, it gets promoted to a piece of higher class. Otherwise the player has an option to mutate the piece into a different piece of the same class. The choice of mutating (or not) must be made at the time the piece is removed. White cannot use the pocket on the first move. The king cannot be placed into the pocket.