Acheron's Fury

Once per day, when you use this spell a burst of fire and necrotic energy burst from you as you grow a pair of decaying wings, each creature you choose within 20ft of you takes 2d10 necrotic and 2d10 fire damage. For the next hour you gain a flying speed of 40ft. At any time during this hour you can expend another spell slot of level 2 or higher to do the damage portion of the spell.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 2d10 (1d10 necrotic and 1d10 fire) for each slot level above 3rd.