Barnabus’ Burning Blast

A bright streak flashes from you to a point you choose within range and then blossoms with a low roar into a fiery explosion. Each creature in a 30-foot-radius Sphere centered on that point makes a Dexterity saving throw, taking 16d6 Fire damage on a failed save or half as much damage on a successful one.

Creatures who fail their Dexterity save against this spell also begin burning, taking an additional 2d6 fire damage at the start of their turns if they do not take an action to douse the flames

This spell doesn’t come without risk however. As noted in the journal entries, barnabus never quite got some things right. There is a 5% chance of instant self immolation, dying instantly, as he just couldn’t quite work out that kink. Roll a D20, on a 1, you get the deal. You may be able to work out a way around this through study or practice casting however.

Using a Higher-Level Spell Slot. The damage increases by 3d6 for each spell slot level above 7