Bone Rattle

The little monster hops along beside you like any other pet. The reason to carry it is how it keeps up. Get far enough ahead of it, or take to the air, and it grabs hold of a floating crimera and gets towed after you, which reads less like a pet catching up and more like a small creature commandeering a flying eyeball.

It comes off the Brain of Cthulhu, which is one of the easier rematches in the game and summonable from materials the crimson hands you by the stack. If the drop does not come on the first kill, just build another summon and go again rather than waiting for a natural spawn.