Underwater Cave QoL - Bubbulb: Glow Lichen Mushroom

As irl lichens are made from a symbiotic partnership of algae and fungus, they can also fruit like standard mushrooms. Incorporating this into gameplay, when spawning underwater, Glow Lichen could grow a new fungi item called Bubbulbs, which are emissive and give off a higher light level depending on the number of bulbs growing on the Glow Lichen. While underwater, any given patch of lichen can spawn with 0-3 bulbs (0 being the most common and higher numbers being rarer) upon world generation or when bone mealing an adjacent patch.

Bubbulbs would act as a sort of early-game Respiration/Water Breathing alternative, though only refilling the player's oxygen instead of giving a lasting effect. They could possibly be used as an ingredient in recipes or as a breeding item, but otherwise super simple just to make submerged caves be less of a pain to explore.

Additionally, it would go a long way for subaquatic exploration if Glow lichen spawned in much larger patches and higher quantities in low light level underwater areas due to how annoying it can be to illuminate and explore larger water-filled caves.