Flamethrower

It sprays a cone that widens as it travels, which makes it a crowd weapon first and a single target weapon a distant second. Invasions are where it earns the slot. The Old One's Army and the Pirate Invasion both funnel dense groups into a lane, and everything in that lane burns at once. Worms are the other standout, since one burst overlaps several segments of the same body.

Ammunition is Gel, which is effectively free once you have a slime farm or a King Slime routine, so there is no reason to be careful with the trigger. Water, honey and Shimmer kill the flames outright, and it will not fire while you are submerged, though it works fine while you are standing in lava. The burn it leaves behind lasts far longer than the flames themselves, so a quick pass over a group keeps ticking after you have moved on.

Speed is worth more than the raw damage roll here. A speed bonus adds an extra stream to every pull of the trigger for the same single unit of gel, and velocity stretches how far the cone reaches before it fades. Unreal covers both, but a Rapid roll is not the downgrade it would be on most guns.