Unstable Explosion

You cause an unstable explosion to erupt at a point of your choice within range, rolling 3d6. For each die that rolls a 6, roll an additional d6 and the radius of the spell expands by 5 feet. Each creature within the final range of the spell must make a Dexterity saving throw. On a failed save, they take fire damage equal to the total value of the rolled dice. On a success the target takes half as much damage.

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d6 for each slot level above 2nd.