Ghoul

Ghouls appear in the underground desert once the world turns Hardmode, and the version you run into depends on what has spread into that stretch of sand. Clean desert produces the plain Ghoul. Corruption growing through the caverns turns them into Vile Ghouls, Crimson into Tainted Ghouls, and Hallow into Dreamer Ghouls. Nothing summons any of them. One desert can hold several kinds at once wherever a band of infection cuts across untouched ground.

All of them just walk at you and swing, the same blunt approach a zombie takes, and on its own that is nothing. What they leave behind is the problem. The Corruption version sets you alight with cursed flames that water refuses to put out. The Crimson version smears you with Ichor and your defense drops for as long as it sticks. The Hallowed one confuses you, which reverses your movement at the exact moment you are trying to climb out of a pit. Any of the three can turn a routine cave trip into a death well into Hardmode gear.

Distance solves them completely, since none of the four has a ranged attack or any way to reach you off the ground. Kill them before they close and the debuffs never happen at all. The real danger is the terrain: desert caverns are cramped and vertical, and being confused or set burning halfway down a shaft with two more waiting at the bottom is how the trip ends. Take the fights in corridors where you can back up, and light a route before you commit to a descent. The infected varieties are also the reason to come down here in the first place, because they carry loot the plain ones do not.

• The word comes from Arabic folklore, where ghouls preyed on people crossing the desert and dug up the dead, so putting them under the dunes is a closer fit than most monster names in the game manage.
• Three of the four can be hit with the same debuff they hand out. The Hallowed one is the exception and cannot be confused.