I ended up making a solid prototype and decided this is a good enough experience for the jam so I won't be finishing or submitting it.

The concept is simple: a puzzle game where your character needs to go to the exit but every time you move, you are generating walls that may get in your way or block off the exit. The way you face determines which way walls will be generated, so you need to pick your path carefully. Future levels could have included spawners that rotate the opposite direction of you, or spawners that remove walls instead of adding them, or reversing what's there, or create bridges over the void or any number of things. And there could be teleporters around too. There are a lot of fun possibilities.

I have a feeling a similar game may already exist so if someone knows of one, please comment. Best of luck to everyone still going!