This is pure speculation but i think the giant purple callus projection is the real callus. The raid sword mentions callus found something that changed him and other raid gear lore mentions how he inherited this power and was now considered a god. What if whatever he met at the edge of the universe the things that is stronger than our feeble light transformed him into a demi god of sorts able to have his own realm with distorted reality. In this realm he can make psion projections ones not bound by the laws of the physical realm able to kill a entire team of guardians able to change the landscape of the arena with his mind as well as puking giant skulls that when hit give guardians a great boost of strength. In my opinion this is only a slight taste of what reborn callus can do if we side with him we may actually transcend the light but at what cost?