Darkball

A pitch-black streak flashes from your pointing finger to a point you choose within range and then blossoms with a low roar into a cloud of magic darkness. Each creature in a 20-foot-radius sphere centered on that point takes 3d6 necrotic damage.

The cloud spreads around corners. 

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d6 for each slot level above 3rd.