Dark Caster

Nothing summons these. They are part of the standing population inside the Dungeon, so once you have opened the place up they appear on their own alongside the skeletons and the bats, with no time of day or moon phase attached. A red hatted version of the same enemy exists, but that one only shows up where the red hat Skeletron puts it, never as a normal spawn.

It plants itself, throws a short burst of spheres, then blinks somewhere else on screen and repeats. The spheres ignore Dungeon brick completely. In a building made almost entirely of narrow rooms and blind corners, that means you take hits from something you never had a line to. Each sphere dies to a single point of damage from anything, so a weapon with any spread at all clears the air in front of you as you walk.

Damaging it while it is winding up cancels the attack outright. One tag from a fast weapon and it teleports away having fired nothing, which makes attack speed worth more here than a big hit. It is still alive somewhere on screen, so this is a way to close the distance safely rather than a way to finish it.

Its shot is nearly the same sprite as the Water Bolt sitting in the bookshelves of the same Dungeon, and casting that spell yourself is how people get killed by their own screen. The tell is walls. Yours stops on brick. Anything swimming through solid stone belongs to the enemy. It matters more later, because in Hardmode on Expert the sphere damage climbs steeply and a stray one that phased in behind you can take most of an endgame health bar.

• The spheres uncover map as they travel, even while buried in rock. Let one fly past instead of popping it and you get a free look at whatever sits on the far side of the Dungeon wall.
• Take the wizard hat off one and you have Tim. The sprites are otherwise the same.
• A Skull worn with a Robe turns your own character into a close match for it.