Maybe each player gets a 3 move cooldown on using the same variant.
New variant: Switchy Chess
Add cooldown of 3 moves and also a 10 second or so chance to decide your variant. If this seems like a way to cheat for extra time do evaluate moves then it could change to be something like your time runs down at a slightly slower pace instead.
Fog of war is a good idea, but I think N-check is not due to situations that might involve perpetual check and is in general just too overpowered; especially if it is not reset every time it is switched to N-check.
It would be pretty hard to implement due to the fact that this introduces new rules and not just a new board and custom position
if its a new variant why don't we just keep the classic ones?
1. 3-Check
2. Crazyhouse
3. Antichess
4. King of the Hill
and some new ones:
5. Fatal Capture (with Bricks maybe)
6. Duck Chess
7. Sideways Pawn
8. Torpedo
1. 3 check is bad.
2. Crazyhouse is also bad for OTB.
3. Antichess would be interesting, but it would really change the dynamic, so be careful if using it.
4.KOTH is great.
5.Fatal is good, but not stonewall.
6.Duck chess would be a great rule to implement at a nice time and save yourself.
7.Sideways pawns is great.
8.Torpedo would be great.
9.PacMan isn't well known, but still it would be a good rule.
10.Don't forget atomic.
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If you include Pac Man, then you shouldn't allow pieces to go back to their starting square.
Also pac-man would never work because then both sides would be in check by the start of the game. Even if you stopped that the the queenside knight could warp and take the black queen off the bat.
What I mean is, if you have a rook on c5, you can make the rook travel around the c file and return back to c5
Pac-man could be restricted to only when all of the pieces(not pawns) have moved to minimize looping behind the defenses but it would still cause a lot of problems.
Google doc of rules