Liber Ex Tabernis Daemonia Eiciens
(Inspired by this)
It is not widely known that demons prefer to possess places and things rather than people – or rather, it is widely known, at least in folklore – but is instead largely ignored in modern society because most people would rather not think too deeply on what the existence of demons implies. Better by far to keep on with keeping the supernatural nicely vague and plausibly deniable, right?
…Yes, that attitude kind of breaks down the moment that the crushed-iced drink machine gets possessed by a being from the Seventh Pit of Ebon Cacophony and then proceeds to spray ectoplasmic-flavored candied slurry all over the place. It’s not even that the demons doing the possessing these days have any real long-term schemes. Possessing your local convenience store is apparently now a vacation for them. They apparently win the right to do so in contests. So demons thus have a vested interest in drawing out the process as long as possible.
Fortunately for the supernatural recalibration industry, this is an old problem, which is why there’s an old book on the subject: the Liber Ex Tabernis Daemonia Eiciens (Ex Tabernis for short). Most copies of Ex Tabernis are handwritten and written in a rather obnoxiously dodgy form of medieval Latin, but an English translation was published in the Victorian era. That copy is largely considered useless as anything except a way to figure out what pages the good cantrips are on in the original – but the Victorian edition still has any number of interesting anecdotes in the Appendix, some of which might even still be relevant today. The Latin edition is strictly for work.
In roleplaying game campaigns where demons are real and can possess both objects and architecture, Ex Tabernis is a plausible source for learning spells that detect demonic possession of either. It will also give hints as to what kind of demon is possessing which kind of item/place, and even some helpful advice on how to perform successful exorcisms. Ex Tabernis is more or less useless when it comes to demons possessing living things, although the text refers to a Liber ab Arboribus as if the reader was expected to know what that was. Lastly, an important safety tip: some of the spells for detecting demonic possession have a problematic side-effect; casting those spells on an area or object free from demonic possession is LOUD, supernaturally speaking.