Darcy's Darken Demise

You exhale a wave of black fog that rushes forward and embraces creatures in a 30 ft cube in front of you.

Each creature of your choice in the cube must make a Constitution saving throw. A creature takes 4d10 necrotic damage on a failed save, or half as much damage on a successful one as the fog draws the creatures life force out of their body.

The fog spreads around corners, and its area is heavily obscured. It lasts until the start of your next turn or until a wind of moderate or greater speed (at least 10 miles per hour) disperses it.

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