Clinger Staff

Point it at a spot and a tall column of cursed flame grows there and stays for minutes without any further input. Anything walking through takes damage and picks up Cursed Inferno on the way. You only ever get one, so casting again relocates the wall rather than adding a second, and the mana cost per cast is the heaviest of any magic weapon in the game. This is not a weapon you spam.

If terrain sits between you and the point you aimed at, nothing spawns at all and the mana is spent regardless. Aim at floor you can actually see. This bites hardest in exactly the cramped places the weapon is otherwise best in.

Tight spaces. Dungeon corridors and the lanes enemies funnel down during the Old One's Army are ideal, because the knockback alone stops most ground enemies from ever reaching you, never mind the burn. Against anything that flies, the fixed height of the column is a hard ceiling, and Skeletron Prime will simply climb above it unless you build a platform stack to cast from higher up. The Nimbus Rod covers similar ground and does not have that problem.

Damage is halved against every worm-type enemy, The Destroyer included. Despite that it is one of the better answers to them, because a long body crossing the flame puts many segments inside it at once and the wall charges each of them separately. The penalty is real and the total still comes out ahead.

The wall locks in its damage at the instant it appears and ignores every buff, swap and accessory change you make afterward. Critical chance works the opposite way, reading off whatever weapon you are currently holding. So the optimal play is to build a high damage loadout purely to throw the wall out, then switch to a magic weapon with an unusually high base critical rate and let the flames inherit it. Sky Fracture, Staff of Earth and Stellar Tune are the usual partners. Because crit comes from elsewhere, Ruthless beats Mythical on the staff itself.

Corrupt Mimics carry it, which puts it opposite Life Drain from the crimson version and Crystal Vile Shard from the hallowed one. Despite the name and the sprite, Clingers have nothing to do with it.