Corrosive Mist

A vicious mist of corrosive acid fills in a 20-foot cube centered on a point within range. 

When a creature enters the spell's area for the first time on a turn or starts its turn there, it is engulfed by the acid, which causes unspeakable pain, and it must make a Constitution saving throw. It takes 4d4 acid damage on a failed save, or half as much on a successful one.

On each of your turns, after you cast this spell, you can use an action to move the mist 30 feet in any direction.

At Higher Levels.  When you cast this spell using a spell slot of 2nd Level or higher, the damage increases by 2d4 for each slot level above 1st.