surge of death

You create a link of necrotic energy with a enemy or object within range, where it explodes in a 10-foot-radius Sphere if it fails a constitution saving trowh. Each creature in that Sphere must succeed on a Dexterity saving throw or take 2d6 necrotic damage. every round for the next 20 rounds as long as you have Concentration, it can pulse out necrotic energy in a 10-foot-radius, dealing 1d6 necrotic damage each time, and halfing their speed.

Spell Upgrade. The damage increases by 1d6 for each level when you cast it at higher levels than third.