Hogwarts schooling

A thick spray of smoke billows out from your wand, filling a 15-foot cube originating from you. This smoke spreads around corners. It lasts for the duration or until strong wind disperses the smoke, ending the spell. Its area is heavily obscured. 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 3d6 poison damage on a failed save, or half as much damage on a successful one. Constructs and undead are immune to this damage.