Biohazard

You coat a 15-foot-wide cube with a toxic sludge for the spell's duration.  The area is difficult terrain and filled with dangerous fumes.  A creature that enters the area or starts its turn there must make a constitution saving throw.  On a failed save, the creature takes 1d8 poison damage and is poisoned until the start of their next turn.  Creatures are affected even if they hold their breath or don't need to breath.

At higher levels.  If you cast this using a spell slot of 3rd level or higher, the damage increases by 1d8 for each slot level above 2nd.