Finn (beatboxing), Jake (playing viola), Princess Bubblegum (playing Beemo as an 8-bit instrument) and Marcelline (playing bass guitar) form a band in order to defeat the Door Lord and recover what was stolen from them.
Note: The episode became somewhat controversial because of an allegedly implied relationship from the past between Marceline and Princess Bubblegum. The accompanying "Mathematical" video recap caused more controversy about these implied lesbian relations between Princess Bubblegum and Marceline by making it seem as if the writing staff actively seeks input from fans. This incident was addressed by the show's producer, Fred Seibert, and the video was pulled.