Empty Cube Chess

One approach was to add a third dimension, but I did not wish to add triaxial moves and sought a really good excuse not to have them. Then I thought, why not hollow out the 3d board, which assuming the one-foot-in-the-grave rule makes such moves impossible. That had the effect of subtracting a 6x6x6 board from an 8x8x8 one - 216 from twice 256. Thus the number of cells is easily calculated as 296.

I then realised that Pawn structure would be far more complex than even on a 2d corner variant, with the same players' Pawns crossing each other. Realising that each face would be initially occupied by one army, and the opposite face by the opposite army to boot, I decided to label one pair of opposite faces Blue, one pair Red, and one pair Yellow for clarity. Each army initially occupies one face of each orientation colour. An exception is that in a 4-player version that I devised later on, in which a different pair of armies share each face.

Since I created this page Kuyan Judith independently created another using the same board, one of the Cube Surface Board Chesses, though with only FIDE pieces.

Setup

Ecumenical MT³, Red faces

Ecumenical MT³, Yellow faces

Wildeurasian MT³, Blue faces

Wildeurasian MT³, Red faces

Wildeurasian MT³, Yellow faces

4-player MT³, each face for a different pair of players and kind of Pawn

Note that in each variant the top and bottom edges of the Blue faces are the left and right edges of the Red, the top and bottom edges of the Red the left and right edges of the Yellow, and the top and bottom edges of the Yellow the left and right edges of the Blue. As there is one King aside, it must clearly be the same one in all three kinds of face!

Pieces

	This group occur in all variants. The KING moves one square orthogonally or diagonally, must be kept out of check. The STEWARD moves likewise but is capturable and restricted to making noncapturing orthogonal moves and capturing diagonal ones. It serves as a fill-in where Pawns would be ambiguous.
+=	This group occur in both variants, and move any number of steps through unoccupied intermediate cells. The ROOK does so along any orthogonal, the colourbound BISHOP along any diagonal, and the QUEEN any of either.
+=	This group occur in both variants, and are orthogonal leapers which cannot be blocked. The colourswitching KNIGHT makes any 2:1 leap, the colourbound CAMEL any 3:1 leap, and the GNU any of either.
	This group occur only in the Ecumenical variant, and are mixed compounds. The MARSHAL combines the Rook and Knight moves, the CANVASSER Rook and Camel ones, the CARDINAL Bishop and Knight ones, and the colourbound CALIPH Bishop and Camel ones.
+=	This group occur only in the Wildeurasian variants, and differ from the Rook, Bishop, and Queen when making a capture, which requires exactly one intervening piece of either army that is not itself captured. The CANNON moves along any orthogonal, the colourbound ARROW along any diagonal, and the TANK any of either.
	All kinds of PAWN move orthogonally except when they capture, which they do diagonally. They always move one step expect in a noncapturing move within their array face. They all move to the nearest or equal-nearest empty-starting edge until they reach it. After that Blue-face Pawns move toward the enemy Blue face, Red-face Pawns toward the enemy Red face, and Yellow-face Pawns toward the enemy Yellow face.

Rules

Castling is allowed in the Ecumenical variant with any Rook, and in the 4-player one with the Rooks sharing an orthogonal with the King. The King always moves 2 steps with the usual restrictions. As with my 2d 2-player corner variants, it is less likely to be of use than in a face-to-face variant, but it is there all the same.

Pawns reaching the enemy counterpart of their own face cannot move within that face unpromoted, which is why they cannot capture an enemy same-face Pawn En Passant. They must immediately be promoted to any other capturable array piece.

In 2-player subvariants Check, Checkmate, and Stalemate are as usual. In the 4-player one a player is Checkmated when their King is threatened by the player about to move. That player's pieces are removed from the game, which continues with the Checkmating player's move.