Toxic Cloud

You create a 20-foot-radius sphere of green, corrosive gas centered on a point within range. 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 acid. On a failed save, the creature begins to burn in the acid, and takes 4d6 poison damage, or half on a failed save.
If the creature also begin it’s turn within the cloud, it takes an additional 1d6  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.