From Introduction:
This game assumes some knowledge of the canonical adventure time universe. The purpose of this section is really to explain the systems in this game in the narrative, and provide a map.
Materials Required To Play
You need a copy of the character sheet for each player playing, this book (of course), and a twenty sided die (sometimes called a d20), or some other way of choosing a random number between one and twenty. And of course, pencils or something else to write with.
Am I supposed to play characters from the show?
You aren’t supposed to and you aren’t supposed to not. If you want to play out an adventure where Peppermint Butler, Pat The Party Bear, and Breakfast Princess solve murder mysteries in the fire kingdom, by all means do so. But if you want to make original characters, that is fine as well.