Unholy Trident

It throws tridents fast and flat, and they move quickly enough that leading a target is barely necessary. Each one punches through a small number of enemies, taking a bite out of its damage on every pass, so the second and third bodies in a line take noticeably less than the first. Lined up in a corridor that is fine. Against a single boss the piercing does nothing for you and you pay the same mana either way.

Red Devils only start appearing in the Underworld once a mechanical boss is down, and they hit hard enough that hunting them on foot is a bad plan. Build a platform, let them come to you, and bring something with reach. The drop is thin enough that you will be there a while regardless.

In those seeds it trades places with the Flower of Fire: the devils stop dropping it entirely and you find it locked away in a Shadow Chest or an Obsidian Lock Box. It gets rebalanced downward to fit the earlier slot, so do not expect the same weapon you remember, but pulling one out of a chest before Hardmode is a real early game magic option.