Breath of Sarkan

You touch one willing creature and imbue it with the power to spew magical energy from its mouth, provided it has one. Until the spell ends, the creature can use an action to exhale radiant energy in a 30-foot cone. Each creature in that area must make a Dexterity saving throw, taking 15d6 radiant damage on a failed save, or half as much damage on a successful one. 

The radiant power of this spell is the only known force that can destroy the spawn of Donar the Corruptor.

At Higher Levels. When you cast this spell using a spell slot of 8th level or higher, the damage increases by 3d6 for each slot level above 7th.