Book of Skulls

The skulls drift out slowly and curve toward anything close by. Once one picks a target it commits, and it will not switch even if something more dangerous walks in front of it. That is fine against a single enemy and frustrating against a group, where half your shots chase whatever was already dying.

They also stop at walls. In the corridors of the Dungeon, which is where you are most likely to be carrying this, that is a real limit, and you often have to close to clear line of sight before firing.

It falls out of Skeletron, so you get it exactly as the Dungeon opens up, and the tracking means you can fire roughly in the right direction while dealing with something else. The projectiles are bright enough to double as a scouting tool in unlit rooms. Against anything fast, the slow travel speed loses badly, and its real competition is whatever else came out of that same fight.