Erebus's Malevolent Mist

You create a 20-foot-radius Sphere of jet black mist centered on a point within range. The Sphere is Heavily Obscured. It lasts for the duration or until a strong wind (such as one created by the spell "Gust of Wind") disperses it.

On contact with Erebus's Malevolent Mist. All living creatures take 4(d8) necrotic damage, and have disadvantage on any attacks while affected by the mist. 

Using a Higher-Level Spell Slot. The mists' radius increases by 20 feet for each spell slot level above 1.