Super Star Shooter

You can put it together the moment your first mechanical boss goes down, which makes it one of the better answers to the other two. It is the direct successor to the Star Cannon and it keeps the same ammunition, so if you have been sitting on stars, the upgrade costs you nothing to feed.

Stars ignore gravity and travel flat, and nothing stops them except a block. They pass through every enemy in the line and keep going. On top of that, each enemy a star damages gets a light slash dropped onto it, and those slashes pierce as well across a small area. The slashes carry no knockback at all, so nothing you hit gets pushed off you, which matters more than it sounds against packs.

Fallen Star supply, not damage, decides how you use this. Stars only fall at night and you have to go collect them by hand, so continuous fire is not a thing. Most people run it as a burst weapon and carry something with cheap ammo for everything else. An Ammo Box or any other conservation effect pays for itself here faster than on almost any other gun. Journey Mode sidesteps the problem entirely through duplication.

This is where it looks broken. Infinite piercing along a segmented body means one shot touches most of the worm, and every segment it touches spawns another slash. Hold a line, keep firing, and the fight ends early.

Post-Plantera ranged options beat it on single targets, but the slashes and the piercing keep it working as a crowd clearer through Golem. Fire into a group rather than at one enemy, and shoot along open space rather than into terrain, since a star that clips a block is gone. Unreal is the modifier to aim for.

The seed turns the weapon inside out. Most bosses reflect the stars back at you, so the thing that made it strong now shoots you instead, and its base damage and fire rate are both worse there before any of that happens. Treat it as unusable against bosses in those worlds.