bad gas

You create a 5-foot-radius sphere of poisonous, yellow-green fog centered on a point you choose within range. The cloud can move 15 feet behind you and stops on the first creature 

When a creature enters the spell's area for the first time on a turn or starts its turn there, that creature must make a Constitution saving throw. The creature takes 2d8 poison damage on a failed save, or half as much damage on a successful one