A mod where the player will randomly spawn with some type of allergy (can change after death). Certain types of food, allergic to grass, sunlight, hay fever, plants, animal fur, lactose intolerance, gluten, metals. Maybe having some type of biome only interaction?
Possibly have some time of medication to suppress them for a certain amount of time?
This mod would be great to force the player to approach the game a bit differently and try out some new things!