Corrosion

You emit a blast of acidic green flames in a 50ft Cone. Each creature within range makes a Dexterity saving throw, taking 3d6 Fire damage and 3d6 Acid damage on a failed save or half as much damage on a successful one.

Using a Higher-Level Spell Slot. The Fire damage and the Acid damage increase by 1d6 for each spell slot level above 4.