A twofold piece is captured if either of its components is captured. We would consider this type of piece to have a size of two. The following diagram shows the squares a twofold Knight could move to. The squares are numbered 1-8, and squares with the same number represent the destination squares for a single move of the twofold knight. In Ganymede Chess , the Wall can be thought of as a twofold rook that also has the option of rotating.
All pieces are twofold pieces.
Pawns promote to either a twofold Queen, Rook, Bishop or Knight. There is no castling. I suspect this game would be fairly awkward, with friendly pieces getting in each other's way too often. These pieces are very similar to twofold pieces, except they occupy a 2x2 matrix of squares. Note however that this piece is more difficult to capture than an ordinary fourfold piece, as all of its squares must be threatened.