The Burning Head

A large laughing skull screams and travels forward and in a line 60 feet long and 10 feet wide in a consuming wake of flame out from you in a direction you choose. Each creature in the area must make a Dexterity saving throw. A creature takes 6d8 fire damage on a failed save, or half as much damage on a successful one. The skull leaves a field of flame in its wake in the area of the spell for 1d4 rounds after the spell has been cast. Creatures and objects in this area take 2d4 fire damage on the start of their turn in the area or the first time they enter the area on a turn. The flames dissipate at the start of the last rolled round.
The giant flaming skull ignites flammable objects in the area that aren't being worn or carried.

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, the damage increases by 1d8 for each slot level above 4th.

(leave a comment if this seems busted or needs changing)