Grotesque Chess, created by Fergus Duniho, is played exactly like Chess except for the introduction of two new pieces, a couple extra Pawns, and a new castling rule. The two new pieces are the Equerry (a compound of Bishop and Knight), which starts in the b file, and the Guard (a compound of Rook and Knight), which starts in the i file. The new castling rule is that the King moves two or more spaces toward the Rook when castling, stopping short of the Rook's space itself, and the Rook moves to the last space the King passed over. Otherwise, the usual castling restrictions apply.
Castling is handled by moving your King to the space it will move to for your castling move. The Rook will then move to its other side.