The Godsmen Apocalypse
The party knows a bit about Pandorym, but there is still much to discover.
What is known is that an ancient group of wizards searched outside of the planes of the multiverse for a force that would destroy the gods. They named the entity “Pandorym” and plotted to use him as a weapon against all deities. The gods struck first separating Pandorym’s mind from his body, sealing his mind in a crystal prison and his body stashed somewhere in the Astral Plane.
He craves to be reunited with his body and carry out the vengeance he was contracted to commit. He has been slowly gaining power and, according to the Sword Archons in Project Satan’s antechamber, he has finally found a mind capable of bearing his will without being destroyed.
The party did witness (through a type of ethereal flashback) the moment that the gods destroyed the civilization that dared summon Pandorym. They obliterated the city in Holy Fire, and the crystallization of Pandorym’s will acted like a sphere of annihilation upon the entire area. Furthermore the gods sealed the entire area away in a demi plane that intersected the Material Plane at only one (unknown) junction.
Considering the demise of so many deities through The Great Divide, it is only common sense that Pandorym would begin gaining strength. Furthermore, the faintest arcane symbols have began appearing in the sky heralding his return.