Bee Gun

Fire in the general direction of trouble and the bees sort themselves out. They drift for a moment before waking up, then chase whatever is closest and re-target if something nearer wanders in. Because they hang around after you stop firing, damage keeps landing while you reposition or drink a potion, which almost no other magic weapon at this stage does.

Each bee lands for very little, and enemy defense comes off every one of those small hits separately. Against anything armored the weapon collapses. A Shark Tooth Necklace or some other armor penetration is close to mandatory if you want it to stay useful past the fight that dropped it. Bees also die on contact with water and lava, which writes off a good chunk of the Jungle and all of the Underworld.

Mana Regeneration Potions beat Mana Potions here, which is backwards from most magic weapons. The gun drinks mana fast and the bees keep working while you stand still to recover, so regeneration matches the rhythm, while chugging potions piles up Mana Sickness and cuts your damage. If you also picked up a Hive Pack, a good share of the swarm comes out as the larger bee, and that is a genuine step up rather than a visual change.