I picked up the Adventure Time Encyclopedia this week (or to give it it's full title: The Adventure Time Encyclopædia: Inhabitants, Lore, Spells, and Ancient Crypt Warnings of the Land of Ooo Circa 19.56 B.G.E. - 501 A.G.E.). If you're not familiar with Adventure Time, this post will give you the basics.
Everyone caught up? Anyway, this encyclopedia purports to be written by Hunson Abadeer, evil Lord of the Nightosphere, though there are humorous annotations by Finn, Jack, and others. It basically gives Abadeer's dismissive take on the people, places, and things of the land of Ooo.
Beyond the setting inspiration, it has another interesting element possibly worth stealing for rpg use. The entries on the major characters have a list of rumors about them. This strikes me as a good thing to write up for NPCs. Maybe some are true and some are false (a random die roll might decide), but in brainstorming you could put down whatever came to mind.