I came across a forthcoming book in a publisher catalog today. It is called Demon Possession in Anglo-Saxon England. The grammatical oddity of the title started me wondering who possessed, or owned, the demons. That gave me an image of CCG-style* demon trading in the 10th century.
From that, an entire magic system (and alternate Earth) based around demons, in which mages buy, sell, and trade demons, has been growing in my head for the last five hours. Joy, as if I needed another world to add to the ultraverse project. 🙂
And I’ve already converted the magic system to the GURPS RPG (3rd or 4th edition) in my head.
* Collectable Card Game, ex. Magic: The Gathering, Pokemon, Yu-Gi-Oh, etc.