|The following information is from the Adventure Time comic book series.|
It may not be part of the same canon or continuity as the animated series.
Issue 29 of the Adventure Time comics.
"Finn and Jake are back in their bodies, but it looks like the damage is done. Will our heroes be able to right everything they’ve done or is Ooo finally lost? With the help of an unlikely source, this day might be saved. Last issue by the talented Jim Rugg (Street Angel, Afrodisiac)!"
Princess Bubblegum has turned everyone into ghosts, so they could beat up some ghosts that were harassing the candy kingdom. Finn and Jake go help Princess Bubblegum.
Comic preview pages and panels