Arcanic Meltdown

The caster of this spell unleashes all of their arcane energy in a final blast. They select a spellcasting class that they have at least one level in, and remove all levels of it. Everything, including inanimate objects, in a 120 feet radius centered on the caster takes and amount of damage equal to the caster's current level in the spellcasting class they are sacrificing, multiplied by the total level of all expended spell slots from that class. The caster then loses all levels in that class, and should that put them at Level 0 they assume the statistics and abilities of a commoner. A creature with magical resistances can choose to make a constitution saving throw against the caster's former spell save DC with disadvantage.