Hey Fish! Hope you're doing well, and happy new year (well, at least in a few days).
I haven't quite had the ability to check this myself, but I was wondering if the water in the Toilet Realm (or at least what I presume is water) interacts with the new fire element/damage over time effect at all. It seems like it'd make some sense for fire-based weapons not to work underwater, and for enemies that are on fire to be extinguished when they interact with water. Perhaps the future elements could also interact with water in some way that affects their usage significantly. (I think you proposed lighting at some point, perhaps it'd become more/less effective underwater, or using lightning while you're in water would deal some self-damage.)
Obviously, I'm aware that implementing that might be a hassle, but it could be a fun mechanic that makes players reconsider what weapons they want to bring for certain areas and encounters, facilitated by the inventory system.