Detonate Soul

4-level Necromancy

Cause a damaged creature's soul to splinter violently. This spell has no effect on creatures with more than half their hit points or creatures without souls. When you target a creature with less than half its hit points with this spell, it must make a Constitution saving throw. On a failure, it suffers 8d6 psychic damage. If this damage reduces the creature to 0 hit points, its body explodes in a 20-foot-radius. Creatures in the radius must make a Dexterity saving throw, suffering 3d6 bludgeoning damage on a failure or half as much on a success. If the original target succeeds its saving throw, it does not detonate regardless of whether the spell dropped it to 0 hit points.
At higher levels: When you cast this spell using a spell slot of 5th level or higher, the initial psychic damage increases by 2d6 for each slot level above 4th.