This spell permits the Necromancer to accelerate the decomposition of a corpse to an alarming degree. So rapidly does the corpse putrefy, that the toxic gases, normally accumulated in dead tissue over time, explode forth from the carcass in a cloud of poisonous vapors.
Whenever you use corpse explosion, you may choose to have it not deal fire damage. If you do, the explosion, instead, releases poison vapors that force the target to make a Fortitude save or be Sickened for 3 rounds. On a successful save, the creature is Sickened for 1 round instead.