This is what the RttToH module booklet has to say about the Apotheosis:
"If his Apotheosis is a success, Acererak will be able to shift his controlling spirit to any undead creature on any world or plane. Acererak would in a sense become the Negative Energy Plane, invesing it with his consciousness. Thus every creature that depends on the Void would be susceptible to the erstwhile demilich complete and utter domination. The destruction of an undead body inhabited by him would merely cause him to skip to another undead creature nearby, or to one on another plane entirely, with equal ease."
Please consider what, of the things below, your nation would know about.
Throughout the Negative Elemental Plane, an exodus is happening. Every sinister creature that ever called it home, is on the march. Rifts open into the astral plane, as file after file of undead journey inexoraly towards the world of Oerth, like vultures to a dying animal.
All over Toril, the undead in that society are quietly liquidating their assets. They sell their homes, their businesses, abandon their responsibilities. Instead, they stock up on any technological marvels and arcane items of power, and... disappear.
Remember all those worlds that have a Tomb of Horrors on them? Acererak threw his nets deep and wide across the multiverse to entrap mighty adventurers and fuel his ascension. Those crypts are no longer passive. The undead of those worlds are swarmind towards it, razing the land in their path. On each of these worlds, report run like wildfire. Of regiments of mighty knights charging at the column of undead, or powerful priests trying to blast them into oblivion. These reports conclude with the story of one of the creatures, usually a humble skeleton, suddenly blazing with unholy green light and turning towards the threat to blast the flesh off their bones. A collective wail of despair resounds throughout the multiverse, as pests become fierce predators overnight.
+ My creatures become incorporeal.
+ My creatures gain a Ghost Touch ability.
+ My creatures become suffused by negative energy, gaining Positive Energy Protection. (no more Holy Cataclysms or Holy water rain, thankyouverymuch)
)
