Cataclysm

The ultimate form of destruction and power this spell was created by the Dark Wizard Thanatos. The spell mimics the effects of the fireball spell, but was created in a way that allowed for an unstable build up of destructive magic by feeding the spell additional spell slots. Causing the spells size, range, and power to increase drastically.

A bright streak flashes from your pointing finger to a point you choose within range and then blossoms with a low roar into an explosion of flame. Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity saving throw. A target takes 8d6 fire damage on a failed save, or half as much damage on a successful one.

The fire spreads around corners. It ignites flammable objects in the area that aren't being worn or carried.

You can add as many additional spell slots as you want, the spell slot(s) you add can not be a higher level than the one used for the initial casting. The spell slot used for the initial casting does not affect the size or range of the spell and increases damage scaling by the normal amount according to the fireball spell.

For every added spell slot after the initial casting the damage increases by 3d6 (3d6 per level, a 3rd level increases the damage by 9d6). Additionally every 3 levels of added spell slots the range increases by 50' and the radius increases by 20'. When calculating spell level for the purposes counterspell the spell starts at the level of it's initial cast, every 3 levels added to the initial cast increase the spells calculated level by 1. If the spells calculated level exceeds 9th level the target must make a check to counterspell it regardless of the spell slot used, using the DC of it's calculated level.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher the damage increases by 1d6 for each slot level above 3rd. The spells size, range, and damage also increase according to the spells you add pass its initial casting as mentioned above.