So I went ahead and did a complete overhaul of the theme list FF created several weeks ago, and I also updated it with new themes from this thread
Here's the link ♡EDIT: Because y naut
Geometric - Somehow make geometric shapes part of your level. (May be better suited to LL's planets and stuff than SM63)
Dream - Literally how has this not been suggested yet, I think it could be p neat
Cyberpunk - This is 4 u brycæ
Steampunk - In the same vein as the previous except not 4 u brycæ
Utopia/Dystopia - self-explanatory; use either/both
Corrupted - Somehow work corruption into your level. Interpret any way you want--people, government, level itself, whatever
Journey - An epic tale or quest
Core - Design a level literally in a circle wrapping around some object or place at the core of the level. Or work backwards, whatever you like.
Also I'm adding categories to the gdoc