"What Was Missing" is the tenth episode of the third season of the American animated television series Adventure Time. The episode was written and storyboarded by Adam Muto and Rebecca Sugar, from a story by Mark Banker, Kent Osborne, Patrick McHale, and series creator Pendleton Ward. It originally aired on Cartoon Network on September 26, 2011. The series follows the adventures of Finn (voiced by Jeremy Shada), a human boy, and his best friend and adoptive brother Jake (voiced by John DiMaggio), a dog with magical powers to change shape and grow and shrink at will. In this episode, Finn, Jake, Princess Bubblegum, and Marceline the Vampire Queen form a band in order to defeat the Door Lord and recover what the creature had stolen from them. Sugar noted that while the episode may appear to be about friendship, it is really about the power of telling the truth, as exemplified by the episode's songs. Episode composer Tim Kiefer played all of the conventional instruments himself, and used unique instruments, like a Game Boy, to make some of the loops heard in the episode. The episode was watched by 2.185 million people and caused a controversy due to the suggestion of an intimate (and possibly romantic) history between Marceline and Bubblegum, a fact that also garnered praise for the episode from several LGBTQ-oriented review sites. Plot Jake and BMO decide to give Finn some "alone time" with him and his piece of Bubblegum's hair, which he acquired in the second season episode "To Cut a Woman's Hair". However, a Door Lord suddenly materializes and snatches the lock, along with Jake's beloved blanket, and BMO's controller. Finn and Jake chase through the creature's various doors, stumbling upon Princess Bubblegum and Marceline, who both appear to be victims of the Door Lord's theft. Finally, the Door Lord jumps through a door that the group is unable to get past. They realize that they must sing a song to pass through the door; the group decides to create a band. Jake gets his viola, and Marceline retrieves her bass. Princess Bubblegum decides to play BMO as an 8-bit instrument, and Finn beat-boxes. Tensions amongst the band members, however, boil over. Marceline sings a song ("I'm Just Your Problem") lamenting her and Bubblegum's estranged relationship, which almost opens the door, due to it being a song based on truth. Marceline and Bubblegum begin arguing,