Draconic Lash

As you hit the target with an unarmed attack, it takes 1d6 Fire damage in addition to the damage from the attack. At the start of each of its turns until the spell ends, the target takes 1d6 Fire damage and then makes a Constitution saving throw. On a failed save, the spell continues. On a successful save, the spell ends.

At later levels. All the damage increases by 1d6 at levels 5 (2d6), 11 (3d6) and 16 (4d6).