Demon Pyre

You focus on your inner flame and generate a ball of chaotic
fire in your hand, you then throw this ball at a point you can see
within range. The ball then explodes in brimstone and lava in a
20’ sphere. Creatures in this sphere make a Dexterity save or take
6d6 fire damage, half on a successful save. This explosion will also
ignite flammable objects in the area that aren’t worn or carried.
Then, the lava from this explosion settles on the ground
beneath this sphere and remains until the start of your next turn.
A creature starting their turn in this lava takes 2d6 fire damage.
At Higher Levels. When you cast this spell using a spell slot
of 4th level or higher, the damage from the explosion increases by
1d6 fire damage for each slot level above 3rd.