Rune Wizard

Not the bolts. His green blasts travel through terrain and cannot be shot down, which sounds worse than it plays, because they are slow to leave his hands and they hurt far less than he does. The danger is his body. Touching him takes an enormous bite out of a hardmode health pool and finishes the job a couple of taps later, and on Master it can be over in one. He never charges you and never tries to make contact, so almost every death here is a player who walked into him in a cramped tunnel.

His whole routine runs on a timer, and damage resets it. He hops to a new spot, spends a moment winding up, fires a set of blasts, then waits. Land a hit anywhere in that and the volley is cancelled and the clock restarts, so a weapon with a high rate of fire holds him in a loop where he does nothing at all. A burn effect ticking on him does the same without needing you to keep the trigger down. Rapid guns, a Piranha Gun and most minions all lock him out comfortably, and every one of those works from outside his reach.

He only appears in the lower half of the caverns. The exact cutoff differs in every world, sitting midway between the floor of the underground and the floor of the Underworld, so there is no fixed depth to memorize. The usable rule of thumb is lava: once pools start turning up regularly in the caves around you, you are inside his band. Remix worlds throw that out and let him spawn at any height in the underground instead.

He does not teleport blindly. He needs a solid block to stand on with clear air above it, no lava directly overhead, a spot inside a square roughly twenty tiles out from you in every direction, and enough distance that he does not land on top of you. The game even predicts where you are heading rather than where you stand when it measures that gap. Platforms and planter boxes do not register as ceiling, which is why he cheerfully materializes inside a platform walkway. If nothing qualifies he stays where he is and starts the cycle again.

He is among the rarest things you can bump into down there, and unlike Tim there is no way to push his odds up. No candle trick, no depth exploit, nothing. You get him by spending time in deep caves and being lucky. A Lifeform Analyzer picks him out, which is the only real tool available, and it is worth wearing while you mine at that depth for exactly this reason. His banner and bestiary entry also need far fewer kills than a normal enemy, an admission that the usual count would be unreasonable.

Both pieces of his outfit, the Rune Hat and the Rune Robe, come off every kill, so a single encounter is the whole set and there is nothing to farm once you have won. Winning is the hard part in a narrow cave. Long range is the answer wherever you have room for it, but the corridors he lives in rarely offer that, so the practical version is getting a fast weapon onto him from the far end of the tunnel and never stopping.

He is Tim grown up, and the game says so outright: the same rough depth, the same idea of an attack, the same trick of dropping a hat and robe nobody else carries, and an entry that calls him Tim's older brother. Only the Dungeon Guardian deals more contact damage than he does, and across the whole game only that and a daytime Empress of Light hit harder with anything.