Arsgomor was an Old One and an ancient enemy of Illyria, whose domain he attempted to seize before being soundly defeated and forcibly entombed in the Deeper Well. Illyria released him at his full power when she destroyed the sarcophagus that sealed him. As Arsgomor intended to reconquer the world, Illyria stood against him. Using the powers she recovered from the Deeper Well, she bound him with plants and used her temporal manipulation abilities to revert him into a fetus. During the confrontation, Arsgomor managed to kill one of Illyria's pet demons.