"Bad Little Boy" is the eleventh episode of the fifth season of the American animated television series Adventure Time.

The show follows the adventures of Finn (Jeremy Shada), a human boy, and his best friend and adoptive brother Jake (John DiMaggio), a dog with magical powers to change shape and grow and shrink at will.

In this episode, Marceline (Olivia Olson) tells the Ice King (Tom Kenny) a fan fiction involving her genderswapped form Marshall Lee (Donald Glover).

Fionna and Cake go after Doctor Prince for stealing the Enchiridion when he is caught by the Ice King (Tom Kenny) and forced to return it and leave.

She begins her tale with Fionna and Cake at their Tree Fort, playing a game that involves hurling an axe at an apple resting on the head of BMO (Niki Yang).

After Marshall Lee verbalizes his inherently evil nature, he grabs hold of Cake and takes her to the nearby graveyard guarded by an army of beatboxing skeletons.

Martin and Ryan respectively return as Fionna and Cake—genderswapped versions of Finn and Jake introduced in the eponymous ninth episode of the third season.

After the success, the writers had to pause and reflect whether a sequel should come from "a personal fire, something to give it real worth", or from audience demand; Ward considered the former reason mostly followed.

In Entertainment Weekly, Darren Franich graded it an A−, designating it as a "brilliant sci-fi", "fantasy", and "musical mash-up".

Club gave it the same grade, writing that because of the short running time, "Fionna and Cake's episodes are filled with what makes this show great".

He said that it reflects a shift from "the sunny whimsy" of the early seasons to "the darker, melancholic elements" as it "further explores the history of Ooo".

He lauded the songs, which he felt were similar to the original Fionna and Cake episode, and ultimately opined that it was "still enjoyable".