Wikipedia
"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.