"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 Marcelline 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 (pictured), to make some of the loops heard in the episode. The episode was watched by 2.185 million people and caused a minor controversy due to the revelation 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.