The following information is from the Adventure Timecomic book series. It may not be part of the same canon or continuity as the animated series.
Adventure Time Vol. 5: Graybles Schmaybles is the fifth graphic novel in the Adventure Time series.
Finn and Jake are about to go on their craziest series of adventures yet...and they don’t even have to leave their living room? After helping Party God with his technical issues, these two best pals discover a tiny cube all by its lonesome in the middle of the woods. Not ones to leave the helpless so...helpless, Finn and Jake take their new friend back to the treehouse and discover that some of the most harmless looking things can be the most dangerous.