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 #38 is the thirty-eighth Adventure Time comic book. This issue features a back-up story titled "Worst Day," which was written by Rachel Edidin and illustrated by Kel McDonald
Magic Man’s hold on Finn is proving to be stronger than anyone had thought and it’s taking the whole crew to band together to help their friend, only this time, there really might be nothing they can do. It’s up to Finn to stand up to Magic Man, if only he could find the bully.