Eater of Worlds

Two things bring it out. Smashing Shadow Orb clusters in a Corruption world calls it on every third orb, which is how most players meet it by accident. The deliberate route is Worm Food, used while you are standing in the Corruption or the Underground Corruption, at any hour. It appears nowhere else on its own. Only one can exist at a time, and a second Worm Food while one is alive is ignored rather than eaten.

This is a chain of separate creatures, not one target. Every segment carries its own health, and cutting the chain in the middle turns one worm into two, each growing a fresh head and tail. All of them have to die before the fight is over.

The parts are not equal. The head deals by far the most contact damage and has the thinnest defense; the tail is the reverse, tough and nearly harmless. Kill a head and that strand slows to a crawl, which is the fastest way to take pressure off yourself. Aim for the ends rather than the middle, because a strand that loses its head or tail does not split, and a strand down to two segments dies completely when either half goes.

It arrives coiled up and takes a moment to unwind before it starts hunting. Every segment is packed into nearly the same space during that window, so a piercing weapon dropped into the coil hits the entire boss at once. A prepared player can end the whole fight there. The Vilethorn is the classic answer, since its projectile sits in place and keeps hitting.

Anything that pierces or covers area does several times its listed work. Spiky Ball piles, whips and fast swinging melee like the Falcon Blade or Terragrim all chew through segments. Grenade throwing is strong in Classic and stops being strong above it, because the higher difficulties hand the worm heavy explosive resistance. Molotov Cocktail flames are dampened as well, and pierce one target fewer.

Since the body has to follow wherever the head went, you can stand beside the train and hit every segment as it files past. Watch for the head looping back into you. Fighting inside a chasm invites being surrounded from three directions at once, which kills quickly in Expert and above, so hollow out a room in advance and set a bed above the fight. A Recall Potion then pulls you straight out of a pile.

Step outside the Corruption and it stops following, burrows down and heads off screen, but it does not vanish instantly. It also refuses to despawn while you are standing in Crimson. You can work with that: cross the biome edge to park the worm at a distance while you drink and heal, watching the boss icon on the minimap so it does not slip away for good. Dying has the same effect, minus the part where you are alive at the end.

Higher difficulties make it larger, faster, and much quicker to accelerate, so the head keeps up with you instead of trailing behind. The real change is Vile Spit. Heads and body segments start firing globs at you, heads firing more as their health drops, body segments only able to fire while above ground and not backed by a wall. Each glob dies to one hit from anything, so holding a flail out or sweeping a whip clears the air in front of you.

Rewards are weighted differently too. More of the ore and scales moves into the Treasure Bag and less comes off individual segments, with Master pushing that furthest, so partial kills are worth less than they are in Classic. The Worm Scarf only exists from Expert upward.

Several doors at once. The Unconscious Man starts appearing so you can rescue the Tavernkeep, and meteorites become able to land, with each further kill raising the chance one falls that night. The Dryad can move in if she could not before, the Merchant adds the Drum Set, the Arms Dealer starts carrying Unholy Arrow after dark, the Angler gains two more quest fish, and the Traveling Merchant can begin bringing the Gray Zapinator.

You do not strictly have to finish it. Segments drop Shadow Scale as they die, so a player who cannot survive the whole thing can still farm enough for Shadow armor and a Nightmare Pickaxe by killing part of it and running for the biome edge.

It is one of the better money sources before Hardmode. Smelting the ore into Demonite Bar and selling the rest of the pile adds up quickly, and Worm Food stays cheap to make; if Vile Mushrooms run dry, the Dryad sells Vile Powder during a Blood Moon. Because every segment rolls loot separately, seasonal drops arrive in heaps, so it is a good target for presents in December and Goodie Bag drops at Halloween. In Hardmode it keeps paying: any segment can drop a Corruption Key, a corrupted Snow biome adds Amarok to the pool, and a corrupted Ocean adds Pirate Map.