Swamp Gas

You create a 30-foot-radius Sphere of foul-smelling sulfurous gas centered on a point within range. The cloud spreads around corners, and its area is lightly 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. On a failed save, the creature has disadvantage on any attack rolls until it's next turn as it's nostrils burn and eyes water from the acrid odor. Creatures that don't need to breathe  automatically succeed on this saving throw.

The cloud is highly flammable, and any source of fire that touches the cloud will cause it to ignite in a flash. Any creature within the cloud when it ignites must make a Dexterity saving throw. On a failed save, the creature takes 4d8 fire damage, and for the next minute takes an additional 1d8 fire damage at the end of its turn unless it uses an action to put itself out. On a successful save, it takes half damage and is not set alight.

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.