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 is 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.

Diabolists will spawn when a Molten Legion Flag is placed inside the dungeon.