Dark Fog

This spell is from the Dark Souls spell collection.

You create a 20-foot-radius sphere of black fog centered on a point within range that seems to sap away the light around it. The cloud spreads around corners, and its area is heavily obscured. The cloud lingers in the air for the duration.

Each creature that is completely within the cloud at the start of its turn must make a Constitution saving throw against poison. On a failed save, the creature takes 2d6 poison damage.

A moderate wind (at least 10 miles per hour) disperses the cloud after 4 rounds. A strong wind (at least 20 miles per hour) disperses it after 1 round.