Armageddon

Unholy terror strikes the battlefield. This is the most destructive spell that can be cast. The sky turns red and all creatures within a five mile radius must make a CON save.

Save DC is 20+ main casting modifier. 

on a failed save they take (120 + (main casting stat modifier D20)) damage. 

On a successful save they take half. 

On a successful save the caster takes zero damage.

The effort and stress of this spell is terrible and if the caster survives they must roll a DC 16 wisdom save. On a failed save they are horrified by the spell and can never cast it again.