Water Bolt

It sits on a dungeon bookshelf disguised as scenery, and only in the lower half of the dungeon, below the middle of the underground layer. The inventory icon is red, which misleads plenty of people, because on a shelf it is a blue book with a yellow band. Three ways to find it, all of which need you standing close enough to open a chest: run the cursor along the shelves and watch for the one book that returns a tooltip, right click every book you pass since only this one pops off, or mine the lot. World generation rolls for it shelf by shelf, so a world can hold several and a world can hold none. Bigger worlds get bigger dungeons and better odds.

Water Bolt Mimics can drop it, which is the safety net for a world where the shelves never produced a copy. They pose as a placed version of the book, so on an unlucky world the thing you are searching for and the enemy that ends the search look identical. The drop is rare enough to treat as a bonus while clearing rather than a plan.

The shot drifts more than it flies. It passes through enemies without stopping, ricochets off walls, and hangs in the air a long time before fading. In an open field that reads as a weak attack, because most of its life is spent traveling through nothing. Put the same shot in a corridor or a sealed arena and it rattles between the walls, crossing the same target again and again. It moves slowly enough to catch one enemy more than once even without a bounce.

Segmented and multi part bosses are where it looks broken for the point in the game you can hold it. Against the Eater of Worlds or the Brain of Cthulhu in a boxed arena, a handful of casts fill the room with rebounding shots that clip every piece on the way through. Packs of ground enemies in a flat valley or a straight tunnel go the same way. The one limit is the invincibility window each hit applies. It is a global one rather than a per weapon one, so pairing a piercing shot with a fast second weapon gives less than the numbers suggest. Mythical is the reforge to chase.

A shot falling into lava bounces back up instead of dying there. It comes off far quicker and burns out proportionally sooner, and it earns extra wall bounces it would not otherwise have had. It only works if the shot was moving downward when it met the surface, and only the first lava bounce changes anything. Over a cavern lava lake or down in the underworld, that turns a slow lobbed shot into a fast one on the way back up, which is worth knowing before you write the weapon off for those trips.

If you spot one near the outer edge of the dungeon you can go in for it early, and it is worth several deaths because nothing else available at that stage is close. A hoik will carry you through the wall. Set a bed just outside so retries cost nothing but time, carry a Recall Potion so a successful grab does not end in a corpse run, and turn autopause on so you can line the pickup up without the dungeon getting a vote.

The particles a shot sheds as it expires light up whatever it passed through, which makes it a quiet way to map a pre-hardmode spider nest from outside. Firing straight up on the surface will bounce a shot off the underside of a floating island, though faster methods exist for that. During a Blood Moon the projectile runs pink through the upper half of the world and stays blue further down. And once you take it off the shelf you cannot put it back as furniture without the tool that places world rubble.