Conflagrate

You harness the ambient and chaotic magic roiling from a character ignited by fire, causing it to explode with intensity. The target, who must currently suffer from the burning condition caused by fire, must make a Constitution saving throw. On a failure, the target takes 18 dice of fire damage, or half as much damage on a successful one. The size of the dice rolled is equal to one larger than the dice from the burning effect (so a d6 burning effect deals d8, a d8 burning effect deals d10, and so on.) After this spell deals its damage, the burning condition is removed.

At Higher Levels. When you cast this spell using a spell slot of 8th level or higher, the damage increases by 4 dice for each slot level above 7th.