Here is the most convoluted and creative chess variant that has probably ever been invented: 5D Chess With Multiverse Time Travel [Steam]. The first merit is that the title describes the game, which also tries to respect the rules of the original chess as much as possible. I found it in a video from Aliensrock, where you can watch some game videos.
|5D chess with time travel.|
In this multidimensional version of chessThere are considered to be five dimensions: the usual three (of which only the usual two on the flat board are used) and then another temporary one and another one of multiple universes, hence 5D.
The moves of the pieces can therefore be the usual ones, but in addition to that, they can travel back in time. In doing so, the pieces attack the opponent's pieces in the past, and if they capture the king, the game is won.
For example, one trick is to move a piece so that it attacks the king in two different positions in the past (for example, a stationary king or in the same row or column) so that a "temporary check" is produced and the next move is checkmate.
To avoid paradoxes, movements to the past sometimes divide the universe into two-time lines, in which one must also play.
You can move the pieces through the 5D, that is, the knight can move two squares in a flat direction of the board and one in time, or the king one square in time (but without moving on the board).
Of course, it is easier to see it than to explain it, so I recommend reviewing the video examples. You can choose the size of the board, using a simplified version with fewer rows and columns and pieces, or conventional chess. You can also play against other players or the computer's artificial intelligence—definitely one of the most ingenious versions I've seen out there.