Xenopopper

The Xenopopper is a Hardmode, post-Plantera gun. It uses bullets as ammunition, but fires a small cloud of four bubbles per shot, which then pop and release bullets that will intersect at the cursor location. It is dropped by the Martian Saucer boss during the Martian Madness event. The Xenopopper's best Modifier is Unreal.

Trivia
This may be a reference to the Bubbline from Cave Story as it acts in the same way.