Crimson Rod

Point it and a small red cloud settles at that spot, raining downward for several minutes. Only one exists at a time, so casting again relocates it rather than doubling up. The projectile will not travel through terrain either, so if there is a ceiling between you and where you aimed, the cloud stops short and hangs somewhere you did not want it.

Rain falls in a thin column, which means open arenas and anything quick simply walk around it. What it wants is enemies coming to you along a fixed path: a Blood Moon, a Goblin Army, a corridor you have dug. Setting the cloud tight against a wall helps a lot, because most ground enemies press themselves into a wall for a moment before turning around. A cloud one tile above a thin floor will also rain through it and hit whatever is underneath.

Whatever your damage stats are the instant the cloud appears is what it uses for its whole life, and nothing you do afterward changes it. Cast from your strongest damage setup and then switch to anything you like. Standing at a Sharpening Station with a melee weapon in hand before you cast is a cheap way to push the rain well past what the rod looks like on paper.

A large hitbox can be struck by more than one droplet at a time. Against a big boss the real damage is a multiple of what the drip rate suggests, which is why this pre-Hardmode rod outperforms weapons that look far stronger.