About the AUEdit
This AU was spawned from recurring fanart. The Adventure Time AU showcases the Big Four (and supporting characters of the fandom) in place of the characters from the show Adventure Time, almost right down to their personalities. The characters often swap roles when the scenario is genderbent for the "Fionna and Cake" story.
The Big FourEdit
Hiccup plays the role of Finn the Human. Logically, this would make Toothless the play the part of Finn's friend and "brother" Jake the Dog. In the genderbent story, he plays the role of Prince Gumball, Princess Bubblegum's male counterpart.
Jack Frost, for his immortality, ice powers and playful demeanor, plays the role of Simon Petrikov, A.K.A The Ice King. Like the Ice King, Jack would repeatedly kidnap Rapunzel (Princess Bubblegum) in a missguided goal for love and companionship. In the genderbent continuity, Jack plays Marshall Lee, Marceline's male counterpart.
Merida plays the role of Flame Princess, a Fire Elemental that is literally made of fire. She's the daughter of the Flame King and girlfriend to Hiccup (Finn). In genderbend AU, she usually plays Cake, Jake's female counterpart.
Rapunzel plays the role of Princess Bubblegum. In the genderbent story, she plays the role of Fionna the Human, Finn's female counterpart. This could be because Jack Frost (Ice King) has an infatuation with Rapunzel (Princess Bubblegum), and would associate his fictional love with his real-world faux love.
Fans like to make Mavis play the role of Marceline, Vampire queen and heir of the Night-o-Sphere. Because so many fans have associated her with this character, she can be considered an official addition to the AU. She has some history with Rapunzel and may have had a relationship beyond friendship.