Magic Missile

It sits in the locked gold chests scattered through the Dungeon, which means you need a key from a dungeon enemy or a biome key you were saving for something else. It is one of a small pool of weapons those chests hold, so a run that opens several is far more reliable than one that opens two. Golden Lock Boxes pulled out of Dungeon Crates draw from the same pool, so a fisherman can get one without fighting a single skeleton.

Hold the button and the missile follows your cursor on a leash, turning wherever you point. Mana only comes out on the initial cast, so you can keep one out as long as you like and your bar refills the whole time you are driving. Release while dragging and it flies off in the direction you were pulling; release with the cursor still and it heads away from you. Either way it stops obeying at that point and hunts for the nearest enemy on its own. Most players fire and let go immediately, which throws away the part of the weapon that makes it interesting.

It threads through a gap one tile wide and lights up everything it passes, and it flies through water and honey without slowing, which the Flamelash cannot manage. Send one down a shaft you have not dug yet and you will know whether the bottom holds a room, a trap corridor or a pool of lava before you commit your body to it. Since holding it costs nothing, scouting this way is free, and in a dungeon that information is worth more than the damage.

The explosion at the end covers a decent patch and it goes off on any block as well as on an enemy, so you can detonate it against a wall and catch whatever is standing behind a single thin layer of brick. That works nicely in exactly the cramped corridors where you found it. The homing has a real range to it once released, so in a fast fight the sensible play is to release early and let the missile do the tracking rather than trying to steer under pressure.

Do not sell a spare. It is a component of the Sky Fracture later on, which is a straightforward hardmode magic weapon and a much better use of the item than the coins.

The name comes from the spell that has been in tabletop fantasy games since the mid seventies, where its defining trait is that it never misses. The homing here is the closest a platformer can get to that promise.