Desert Spirit

There is no summon for these and no event. They spawn in an Underground Desert that has been taken over by Corruption or Crimson, which means they cannot exist before Hardmode and cannot exist in a desert you have kept clean. If you want to farm one, you have to let the evil reach a desert first, or carry it there yourself.

It blinks in, seeds a handful of slow orbs that home toward you, and vanishes again. The orbs themselves cannot hurt you. They pass straight through walls, gain speed as they travel, and then detonate on a timer, and the detonation is the part that does the damage. So the fight is about where you will be three seconds from now, not where the orbs are at this moment. Blocks are no help whatsoever, and the first orb of a volley takes noticeably longer to come out than the four behind it, which is easy to misread as it being finished.

Landing damage on it will usually cut the volley short and force an early teleport with nothing fired. It never stands and trades, so constant pressure is the whole answer. Trying to out-position it instead means eating a full set of curses every cycle, and in a corrupted underground desert you are rarely fighting one on its own.

It can only reappear on a solid unactuated block with clear headroom above it, inside a square centered on you, and never right on top of you: the game even predicts where you are heading before it picks the spot. If it cannot find anywhere legal it simply does not move. That gives you a way to fight on your terms. A low ceiling over the area you are standing in removes most of the valid destinations nearby. Platforms and planter boxes are the exception worth remembering, since they count as ground to stand on but not as an obstruction, so a farm floored with platforms lets them arrive inside it.

It is a jinn, and the Desert Spirit Lamp it leaves behind points straight at the Aladdin story, where rubbing the lamp binds the spirit inside to whoever holds it. Here the binding has clearly gone wrong.