Diagonal Moves only chess is a variant, in which only diagonal moves are possible, because one player has 32 bishops on the same color squares. The other rules for the starting position are as follows
1. The player with 32 bishops on the same color squares is allowed to either have exactly 5 queens, or exactly 5 additional bishops, in addition to the king, but all moveable pieces, for a player, with the exception of the king must be of the same type.
2. The player that does not have the 32 bishops on the same color squares is only allowed to have 5 bishops plus the king.
3. The starting position must be rotationally symmetric with respect to the pieces that can actually move.
4. The starting position must be one, in which the player to make the first move has no legal captures available, on the first move.
5. The starting position must be one, in which the player to make the first move has no legal checks available, on the first move.
There are 32 starting positions in this variant if you require white to go first or consider changing who's turn it is to not change the position, and 64 starting positions in this variant if you don't require white to go first and consider changing who's turn it is to change the position. All starting positions in this variant are symmetric to each other, with respect to how the pieces move.
This is an example of a game in this variant
1. The player with 32 bishops on the same color squares is allowed to either have exactly 5 queens, or exactly 5 additional bishops, in addition to the king, but all moveable pieces, for a player, with the exception of the king must be of the same type.
2. The player that does not have the 32 bishops on the same color squares is only allowed to have 5 bishops plus the king.
3. The starting position must be rotationally symmetric with respect to the pieces that can actually move.
4. The starting position must be one, in which the player to make the first move has no legal captures available, on the first move.
5. The starting position must be one, in which the player to make the first move has no legal checks available, on the first move.
There are 32 starting positions in this variant if you require white to go first or consider changing who's turn it is to not change the position, and 64 starting positions in this variant if you don't require white to go first and consider changing who's turn it is to change the position. All starting positions in this variant are symmetric to each other, with respect to how the pieces move.
This is an example of a game in this variant