All the Chess pieces are attending a masked ball. Each player begins with a normal set of Chess pieces. A piece must use one turn to unmask, that is to replace a Mask with one of the unused pieces. After a piece has unmasked, it may move about normally. The players must use their first turn to unmask their Kings. Capturing Masks is certainly possible, as this reduces the opponent's potential to add new pieces to the board.
 
A Pawn may make a two-step move from both the first and second ranks. This effects En-Passant captures as well. Castling is naturally impossible. Other than this, all other Chess rules apply.