Lava

Lava takes over from water below a certain depth, somewhere in the lower half of the cavern layer, and covers large parts of the Underworld. The exact cutoff differs from world to world by hundreds of feet, so treat any depth figure as an average rather than a line you can rely on. Small pools also appear around the fringes of the underground desert, sometimes only a couple of hundred feet down.

Contact costs a flat 80 health and sets On Fire!. That number ignores damage variance, so unlike nearly everything else in the game it lands for exactly the same amount every time, though defense and damage reduction still apply. Enemies, town NPCs and critters take a smaller fixed hit. You cannot drown in lava, so the only clock running is the immunity bar.

Two separate systems keep you alive, and they stack. The first is a bank of immunity time. The lava charm, molten charm, magma skull, molten skull rose, lava waders, terraspark boots and the demonic hellcart each carry seven seconds, and running several at once adds them together up to 49. It behaves like the breath meter but starts the instant you touch lava and refills far more slowly once you climb out.

The second is damage reduction. The obsidian rose drops the base hit from 80 to 35 and halves the burn. The Ash Wood armor set bonus halves the hit to 40 and halves the burn as well. Wear both together and lava stops hurting entirely, which is cheaper to assemble than it sounds and turns Underworld building into a non event. An obsidian skin potion gives the same immunity for its duration, and superheated blood summons a mount that is immune outright and fast in liquid on top of it.

Lava deletes low value dropped items once they sink past their own midpoint, and every coin falls in that band. It also knocks loose most placed furniture and platforms and burns most trees. The exception list is long enough to build around: obsidian and ash wood furniture survive, along with obsidian platforms and ash wood platforms, chests, pressure plates and timers, pumps, most statues, minecart track and pylons.

Blocks cannot be placed directly into lava, but falling blocks can. Drop silt or sand in and it stacks up from the bottom until you have a bridge. Mine that bridge away later and the lava comes straight back, unless you have reloaded the world in between and the settle pass has already deleted it.

Because destruction depends on the height of an item's sprite, a lava pit can be tuned to burn junk and spare everything else. Copper coins are the shortest common drop at ten pixels; silver coins are twelve. Fill until a copper coin thrown in burns and a silver one does not, and you have a moat that clears the worthless output of a farm and leaves the rest floating.

The working ratio is one bucket per six to eight tiles of pit length, which means some lengths cannot be hit cleanly at all: 1 to 5, 9 to 11 and exactly 17 tiles land between ratios. Anything 18 tiles or longer can always be filled correctly. On a long moat, walk the buckets along its length instead of dumping them in one spot, because the flow will not level itself out reliably.

The reason to bother is the world's item budget. Past roughly 400 loose items the oldest start vanishing, and a farm producing endless copper stacks will eat that budget and take your rare drops with it. One warning: the Lihzahrd Power Cell is exactly as tall as a copper coin and burns alongside them.

A shallow layer of lava under a farm floor kills walking enemies as they path toward you and gathers their drops into one place. Standing below the pit pulls most of the map into it, including some fliers that dive at you. Keep it shallow enough that it never reaches your own feet, and set the depth by the coin test above so it cleans up as it kills.

Outside a farm, lava is a poor landing pad but not a fatal one. Falling into it cancels the fall damage entirely, so a hellevator ending in lava kills you only if you cannot climb out.

• Lava evaporates after flowing about 50 tiles sideways, so a source you break loose eventually cleans itself up.
• Lavafalls pouring over a half block, and the drips from ceilings, are visual only and harmless. You can place your own with a magic lava dropper.
• Underworld natives, most bosses and anything that phases through blocks take nothing from lava. King Slime and Golem are the two bosses that do.
• The flipper, flipper potion and water walking potion all work on lava as well as water.
• Rain will not turn lava into obsidian, and lava blocks grass from spreading within about two tiles.
• Mining hellstone releases lava, twice as much in Expert, so never break a block while standing under it.
• Fishing in lava needs the hotline fishing hook, the lavaproof fishing hook or bait native to the Underworld, and the catch table is its own.