Managed to stay up long enough to see the theme reveal last night, but I ended up sleeping on it while I considered ideas. Now that a good half a day has passed, I think I've settled on a concept: a procedurally generated dungeon crawler where after each floor you can increase your remaining/total health by selecting difficulty increases for the next one - instead of spending your life to access things, you're earning it by challenging yourself, and the difficulty naturally scales as you either take damage or increase the complexity of the dungeon.

It's possibly not the most original idea in the world, but all of the gameplay elements are relatively straightforward such that I should hopefully have a shot at making this work before the end of the event.