Diabolist

About
Diabolists spawn in dungeons after hardmode is activated. They rapidly teleport and fire blazing magic bolts at you that go through walls. The bolts then explode where they hit and create an "Inferno" - a large flaming ball that does massive damage. Diabolists' spells can go through walls, so make sure there are no walls between you and the Diabolist. Diabolists, like other hard-mode caster monsters in the dungeon will teleport on each hit, making them more difficult to dispatch.

They are immune to the Poisoned and Venom debuffs.

They spawn in dungeons with Tiled Wall.

Multiple tests have proven that they spawn much more frequently when the player is moving, and not waiting in a stationary position.