Mad Mage

What would D&D be without a mad mage? In this case, the mad mage is Mandilissimar. He is a wizard that has based himself in a crumbling tower high in the eastern mountains. He has spent long years searching for an artifact rumored to have been concealed somewhere in these peaks. Over the years, much of his tower has collapse around him from disuse and lack of upkeep. The main floor, a basement level, and the upper chamber of the tower are all that remain intact. The strength of his magic may be the only thing holding the tower together at this point.
In the last two years, he became aware of a haunted manor built on a ledge overlooking the breadth of the valley from a partially secluded spur. Long avoided by anyone because of the undead crawling the hillside around it, Mandilissimar became obsessed with unlocking its mysteries. Anything imbued with that much magic must be done with purpose, and he expected it to be the location of the artifact he sought.
Using his magic to protect him, he moved into the abandoned manor, which was oddly preserved. For a manor that had been abandoned to the elements over 300 years ago, the building showed no signs of decay or the encroachment of nature. Over the last year, Mandilissimar searched every inch of the manor, increasingly convinced that it held some telling secret that he needed to unlock. Yet he has been unable to uncover anything.
He has, however, been constantly bombarded by voices urging him to continue, suggesting ideas of research and guiding his actions. The madness is pervasive inside the manor, and Mandilissimar's reason has begun to slip away. He has become convinced that the key to unlocking the manor's secret will only be revealed under the light of the full moon, which is coming up during the party's visit. To that end, he has prepared a series of elixirs to enhance the senses and aid in the revelation of the key.
Behind all of this is a far deadlier reality. The manor is the former estate of a powerful wizard that became a lich, gathering undead forces to it and terrorizing the valley below. Somewhere along the way, its appetite ceased to get fed regularly, and it became a demilich. Its phylactery is concealed within the manor grounds, but the lich had gotten complacent, and without souls, become a demilich. 80 years ago, some brave adventurers had defeated the demilich, but left without locating its phylactery. Fortunately, they had the foresight to magically trap the demilich's skull in another container on the grounds, so that when it awoke, it was trapped and unable to escape. It used its power to draw undead beings to the manor, and lure Mandilissimar as well. It has been whispering to him in his dreams, encouraging him to embrace the dark magical arts of necromancy, and slowly driving him mad.
Tomorrow, I'll finish up with the backstory, and lay out the bones of this encounter.