Dimension X

Chess in the Twilight Zone. From the introduction:

"This game consists of two parallel planes of existence. On one plane we have a typical chessboard; on the other plane (Dimension X) we have a board inhabited by strange trans-dimensional chess pieces in the form of snakes, spiders and crabs. These creatures can leave Dimension X, and also return to it..."

The rules of the game are simple. The goal is to checkmate your opponent's king. You start with 2 chess boards next to each other. On one board, you play a normal chess game, making 1 move per turn. On the other board each player has 3 short range pieces - creatures with strange powers - that may only move in Dimension X and only attack in our dimension. Each player, during his or her turn, also either moves one of the Dimension X creatures on the second board, crosses between dimensions, or attacks with a creature in our dimension.

This is a most unusual 3D chess variant that quite literally adds a whole other level of tactics and strategy to chess, with a twist.