Woahhh the fully opaque tiles are kinda strategic when it comes to checkmates! I was goofing around with the pieces when all of a sudden, I unexpectedly saw a victory screen pop up- but then I realized- you can't touch pieces that are in the fully opaque tiles! The queen was borderline invincible for that play!
I imagined the tiles like stone tile blocks that crack whenever you step on them, and when they get stepped on three times, it creates a pit. I think the game is technical enough, but I expected the pieces to fall through the hole when stationary over the "pit". It would be awesome to have a mechanic where if you don't move the pieces off the pit in the next turn, it falls.
Additionally, It would be interesting to have a mechanic where if a piece is over the pit, and gets taken, both fall down the pit! (and maybe for those instances, it can weaken the ground around it too!)
Like the other comments, the lack of AI does make it harder to access the game, though I do like your potential thoughtfulness for a multiplayer experience. It definitely differentiates this game from most of the entries for the jam.