Beholder

Beholder is a Pre-Hardmode mini-boss that spawns in the Marble Cave mini-biome.

It can be detected with an Lifeform Analyzer.

Spawn
Beholders will spawn naturally in or near the Marble Cave after the Eater of Worlds or Brain of Cthulhu has been defeated.

Behavior
It will constantly fly around the player and dash forward. Upon contact, it will siphon the player's mana, draining up to 60 points, and inflict them with the Bleeding debuff. It will also occasionally randomly teleport, becoming stationary and shooting five ricocheting fireballs at the player, which inflict the On Fire! debuff.