Re-save each turn while in the cloud (once per turn).
Casting Time
Action
Range
120 feet
Duration
Concentration (up to 10 minutes)
Components
V, S
You create a 20-foot-radius Sphere of yellow-green fog centered on a point within range. The fog lasts for the duration or until strong wind (such as the one created by Gust of Wind) disperses it, ending the spell. Its area is Heavily Obscured.
Each creature in the Sphere makes a Constitution saving throw, taking 5d8Poison damage on a failed save or half as much damage on a successful one. A creature must also make this save when the Sphere moves into its space and when it enters the Sphere or ends its turn there. A creature makes this save only once per turn.
The Sphere moves 10 feet away from you at the start of each of your turns.
Using a Higher-Level Spell Slot
The damage increases by 1d8 for each spell slot level above 5.