"Incendium" is the twenty-sixth and final 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, Patrick McHale, Kent Osborne, and Pendleton Ward. It originally aired on Cartoon Network on February 13, 2012. The episode guest stars Keith David, and also features Jessica DiCicco, who would go on to play the recurring role of Flame Princess.
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, Jake seeks the Flame King's (voiced by David) consent for Finn to date his daughter, Flame Princess (voiced by DiCicco) in order to help a brokenhearted Finn. Jake eventually angers the princess, however, and she chases him back to the tree fort and confronts Finn himself. The episode's plot would be continued in the season four premiere "Hot to the Touch".
The impetus for this episode was the writers and producers not wanting to keep writing episodes in which Finn is continuously rejected by Princess Bubblegum. The character of Flame Princess was largely designed by Sugar, based on a rough drawing by storyboard revisionist and character designer Natasha Allegri. The episode received largely positive reviews from critics, with both David's and DiCicco's voice work earning praise.
Plot
After Princess Bubblegum (voiced by Hynden Walch) scorns his advances, Finn falls into a serious depression and sings a woeful song about the romantic pain he feels, called "All Gummed Up Inside". Jake, worried about his brother, decides to find Finn a new love interest, and so he journeys to the Fire Kingdom, ruled by the evil Flame King (voiced by Keith David).
Jake bluffs that he is an emissary of "Prince Finn", ruler of the Grasslands. Jake attempts to court Flame King's daughter, Flame Princess (voiced by Jessica DiCicco) on Finn's behalf. After several disastrous attempts, including a performance of a song called "All Warmed Up Inside", Jake is told to leave. However, he uses his shape-shifting abilities to morph part of his body and make it look as if Finn has entered the palace. Jake-as-Finn then pretends to strangle Jake, which appeases Flame King. He applauds Finn's supposed butchery, agreeing to give him the hand of his evil daughter.
Jake, distressed that Flame Princess is apparently evil, flees back to the Tree Fort, with the princess on his trails. Once there, Jake tries to explain what happened to Finn, but a struggle breaks out. In the confusion, Flame Princess is nearly killed by rain, but Finn saves her. When she regains her powers, she slaps him, warning him never to mess with her. The episode concludes with Finn noting that he now has a crush on Flame Princess.
Production
"Incendium" was written and storyboarded by Adam Muto and Rebecca Sugar from a story developed by Mark Banker, Patrick McHale, Osborne, and series creator Pendleton Ward. This was both the last episode to have been boarded by Sugar and Muto as a team, as well as the last to credit Muto as a storyboard artist; he was later promoted to creative director for the entirety of season four, as well as the first half of season five.
The impetus for this episode was the writers and producers not wanting to keep writing episodes in which Finn is continuously rejected by Princess Bubblegum. Because of the thematic undertones of romance and unrequited love, the episode had several emotional beats. Sugar later explained that, since she had first started on the show, she had attempted to storyboard a situation causing Finn to cry. Ward and the producers had vetoed this idea several times, because they felt it did not fit his personality. However, with "Incendium", Sugar noted that "the dam finally broke" and she was allowed to make Finn cry over his unreciprocated love of Princess Bubblegum. Sugar put as much "gut-wrenching imagery" at the start of the episode in order to emphasize the installment's pathos. Similarly, she "wanted to make Finn lose it" near the end to show how much his love of Princess Bubblegum was hurting him. As such, the fact that Finn chooses to save Flame Princess over the lock bubblegum's hair was used as a metaphor by the writers to show that Finn was getting over his fixation with Bubblegum.