Orange Zapinator

The Traveling Merchant carries it, and only after the world has turned hard. It is not cheap by the standards of when it first shows up, and since his stock rotates you may need several visits before it appears. The moment hardmode begins he stops offering the Gray Zapinator entirely and this replaces it. If you want one for a collection, buy it before you break an altar.

Every hit rerolls what the beam does next. The baseline is that it slows down and loses a slice of its damage and knockback, and on top of that it draws from a bag of special effects, some of which push damage and knockback the other way. Because those rolls happen on every enemy the beam touches, and it can touch several before it expires, the modifiers compound. A beam that gets lucky twice in a row comes back around hitting for numbers nothing else at that stage of a run can approach. There is no aiming for that, and your damage over any given minute is wildly uneven.

The trail behind the leading edge is decoration. Enemies can stand inside it without taking a scratch, which catches people out firing into a crowd. It also means the slow beams that turn up constantly are the good outcome against a large, predictable target, since the leading edge keeps grinding into the same body instead of sailing past. Plantera is the obvious customer. The beam gives up after it has hit a handful of enemies or after a minute in the air, whichever comes first.

A full Meteor set makes this cost nothing to fire, which sounds like a pre-hardmode combination that has aged out and is actually very good for the messy stretch just after the Wall of Flesh. Free shots turn the randomness from a resource problem into a patience problem, and any armor that boosts magic power multiplies every lucky roll along with the unlucky ones.

Once Golem is down, put this away before you go anywhere near the Dungeon entrance. The shots wander badly enough to clip a robed figure by accident and start a boss fight you had not prepared for. That is the single most expensive thing this weapon can do to you.

The shape and color copy the NES light gun in its later orange form, recolored because laws in Europe and North America forbid toy guns that look real. The tooltip suggesting the thing might be broken is a nod at how unreliable those light guns actually were. The weapon itself began life as a developer tool for killing enemies instantly during testing, got pulled from the game almost immediately, resurfaced years later on a handheld release, and finally came back properly in the 1.4 update as this pair of guns.