Gills Potion

The breath meter simply stops mattering, so you can work underwater as long as you like. Ocean floor chests, a flooded cave system, an aquarium build you are laying tile by tile: all of it stops being a series of panicked trips to the surface. It also lets you wear a Fish Bowl on your head without the game slowly killing you for it.

It is not a lava solution. You never drown in lava, so this does nothing there. What you want for lava is damage immunity and something that lets you move in it, which are different items entirely.

In a For the Worthy world the effect is inverted: while the buff is running you can only breathe in liquid, and standing in open air suffocates you. Drink it once you are already going under, and cancel it manually before you climb out.