Underfire Spark

A palm-sized ball of black flame forms in the hand. It emits no heat or light, and has the same weight as a shadow. A thin mist of black smoke rolls off of the flames and down, like the mist from dry ice. Small sparks are spit from it continuously, making it look volatile.

Make a ranged spell attack. On a hit, the target takes 1d10 necrotic damage. Wherever the flames touch a creature's flesh, the skin boils and pulls away, as if it is rotting very quickly. 

This spell's damage increases by 1d10 when you reach 5th level (2d10), 11th level (3d10), and 17th level (4d10).