The entities of the 7th sphere, the demons, are among the most fearsome creatures a group of adventurers can encounter. Their versatile abilities and fighting power make them unpredictable opponents.
The Catalogus Heptasphaericum describes several dozen of the best-known and some lesser-known demons in an entertaining way, listing their strengths and weaknesses and what you need to do to summon them.
The author of the in-game book is the black mage and demonologist Magister Demirion Ophenos from Mengbilla. He has written his book as a textbook for students and inquisitive minds who need an overview of the basic workings of demons and their summoning.
Ophenos is aware that he does not know as much about some entities as he would like to. For this reason, he has repeatedly allowed other luminaries of demonology to have their say and printed their correspondence in his work.
In addition to demons, Ophenos also describes potential countermeasures, such as banishing and protective circles, anti-magic and other ways of keeping dangerous creatures at bay.