Fire Imp

Nothing summons a Fire Imp and nothing gates it. It is part of the standard Underworld population, and a sizable part of it, so any hellstone mining trip produces a steady stream of them. If you want them on demand, an Imp Statue beats waiting on natural spawns by a wide margin, which is the usual route to an Obsidian Rose and a pile of banners along the way.

This is a caster, so it fights on a loop instead of chasing. It blinks in somewhere on your screen, takes a moment to wind up, throws three fireballs, waits, then vanishes and starts again from a new angle. It will not close the distance and it will not hold still long enough to be a simple target. What kills people is being caught mid jump between the arrival and the first shot.

The fireballs pass straight through terrain. Ducking behind a wall of obsidian achieves nothing, and neither does digging into the ceiling to break line of sight. Cover is not the answer here.

The projectiles can be destroyed. Anything that deals damage pops them, including a minion, a whip, a tool, or a pet that happens to be in the way. That is the real counter and it works passively, since a summon or two out while you mine will clear most of what gets thrown at you with no input from you. Letting one through risks On Fire, which is a slow burn you then carry around a biome made of lava.

The teleport is picky, and knowing the rules lets you pick ground that starves it of places to appear.

• It has to arrive on a solid block that has not been actuated, with clear space above it. A low ceiling removes the spot entirely.
• It will not land on a tile with lava sitting directly above it.
• It only picks spots reasonably close to you, and never right on top of you. The game even predicts where you are heading so it does not drop into your lap.
• Platforms and planter boxes count as valid ground but do not satisfy the headroom check, so an imp can materialize inside a platform floor.
• If nothing qualifies, it gives up, stays put, and starts the cycle over. A tight stone corridor with a low roof is genuinely hostile to it.

Landing a hit resets its cooldown and stops it firing until the next teleport. Anything with steady repeated damage therefore holds it in a loop where it never completes a volley. A handful of minions manages this on its own, which is why summoners barely notice these while everyone else is dodging fireballs through walls.

In For the Worthy worlds the Wall of Flesh brings imps with it, spawning them beside whoever is closest, a few at a time, every couple of seconds. Every part of them is worse. They carry more defense, and more health on Expert and above. They teleport and wind up much faster. Worst of all, their fireballs cannot be destroyed and travel several times quicker, so the shoot-them-out-of-the-air answer is gone completely. Plan on outrunning them, and treat the hell bridge as a dodging problem rather than a shooting one.

The Plumber's Hat and the Obsidian Rose both come off this enemy, and both point the same direction: a fireball throwing enemy, a fire flower, a plumber's cap. Old mobile builds went further and dropped a green cap for the other brother, though that one quietly disappeared.