After a string of Level 5 Manifestations all tied to transmutation, Kylie eventually identified the entity responsible, Cernunnos, in "Powers of Darkness." The book confirmed Cernunnos' modus operandi was transmutation and he needed a human conduit to channel his energy. 
Kylie Griffin used a copy of "Powers of Darkness" during her two and a half hour search to identify and gather information on the Hungry Manitou for the Ghostbusters. The copy of Powers of Darkness is later left on the table left of the microscope in the Firehouse R&D Laboratory.
- Kylie Griffin (1997). Extreme Ghostbusters- Witchy Woman (1997) (DVD ts. 12:26-12:34, 12:38-12:40). Sony Pictures Home Entertainment. Kylie says: "I think it's this being called Cernunnos. First off, he needs a human conduit to channel his energy. Someone has to actually summon him...And then there's his M.O. - transmutations."