necrotic eruption

6-level Necromancy

You cause the cyst of a subject already harboring a necrotic cyst to explosively enlarge itself at the expense of the subject's body tissue, forcing the target to make a Constitution saving throw.   If the subject succeeds on his saving throw, he takes 6d6 points of damage per level (maximum 15d6), and half the damage is considered vile damage (see necrotic bloat).   The subject's cyst-derived saving throw penalty against effects from the school of necromancy applies.   If the subject fails his saving throw, the cyst expands beyond control, killing the subject.   All creatures within 20 feet of the subject take 6d6 points of damage per level (maximum 15d6; Dexterity save half), and half the damage taken is considered vile damage.   All creatures in range that take this secondary damage are also exposed to the effect of the base necrotic cyst spell.   On the round following the subject's death, the cyst exits the flesh of the slain subject as a free-willed undead called a Skulking Cyst.
At higher levels: When you cast this spell using a spell slot of 7th level or higher, the spell deals 1d6 more damage for each slot above 6th.