Crystal Serpent

The bolt itself does very little. What matters is the burst when it connects with an enemy or a wall, which throws out a handful of smaller sparks that fall and skip around the impact point. Firing at the ground or a block just in front of a crowd is often better than aiming at anything directly, because the fragments cover more space than the bolt ever will.

It comes out of a fishing rod in the Hallow with no boss standing in the way, so a mage can be holding one within minutes of the world turning. Nothing else at that point puts out this much area damage. It is also unusually good against enemies with several hittable parts: the fragments spread across Skeletron Prime and his limbs instead of picking one, and large slow enemies eat close to the whole burst per shot.

The sparks die quickly and fall as they travel, so effective range is short and anything that keeps its distance takes only the bolt. This is a brawler's weapon. Each biome has its own version of the idea, with the Toxikarp, the Bladetongue and the Barnacle Staff filling the same slot elsewhere.