Furnace Spitter is a ranged worm enemy. At the lowest Threat it has 42 health, hits for 10 and carries 0 armor. It moves at 2.4, can reach you from 10 away, and telegraphs each swing for 15 ticks before it lands, then waits 30 before the next one.

It is part of the shared Demon Gate crowd rather than any one biome, so it can show up almost anywhere.

Killing it pays 9 XP, and it drops something 5% of the time.