Boil Blood

You channel a dark energy into a living being causing a massive spike in body temperature to the point where one's blood would boil. 

A targeted creature makes a Constitution Saving throw. It takes 10d6 Necrotic and 6d6 Fire damage on a failed save, and half as much damage on a successful save. If this damage reduces the target creature's hit points to 0, their skin starts to bubble as their body slowly broils itself, eventually exploding from the gases trapped inside.

A corpse will explode after 5 rounds, and any creature within a 15 foot radius must make a Dexterity saving throw against your spell save DC. The target takes 6d6 Fire damage on a Failed save, or half of that on a successful save. 

A creature who survives this spell will be heavily scarred, their veins charred from the intense heat. With these horrific injuries, the target creature has a permanent -2 penalty to Strength, Dexterity, and Constitution scores. The creature also gains disadvantage on saving throws and attack rolls while afflicted. This effect can be cured only by means of a Greater Restoration or a Wish spell.