Red's Throw

Any Hardmode boss bag in Expert can hand this over, Queen Slime aside, which means the first mechanical boss you beat may end your yoyo progression on the spot. Nothing you would craft or fish up later improves on it.

It matches the Valkyrie Yoyo, the drop you would otherwise be farming Hallowed Mimics for, so the gain here is timing rather than raw power. Put a counterweight and the yoyo bag behind it and you get a weapon you can park inside a boss while you spend your whole attention on dodging.

It belongs to Red's set, the developer gear named for the game's lead. A yoyo is not an arbitrary pick for him either, since he collects them.