The entry also saw the return of Miguel Ferrer, Steve Agee, Duncan Trussell, and Maurice LaMarche as various characters.

In this episode, the Ice King reverts to Simon (both voiced by Tom Kenny) after being exposed to an anti-magic being named Bella Noche, and gets help from Finn, Jake, and Marceline in order to get Betty, his former fiancée, back.

[2] In the fourth season episode "I Remember You", it was revealed that the Ice King and 1000-year-old Marceline the Vampire Queen had originally met following the events of the mysterious Mushroom War, a cataclysmic war that destroyed modern human society, and "Simon & Marcy" revealed that the two shared a father-daughter bond.

Simon, initially unaware of where he is, steals a magic carpet from Ash (voiced by Steve Agee), flies to the Ice Kingdom, and enters a hidden sanctum wherein elements of his previous life—such as books, artifacts, and his clothing—have been preserved.

On the way, Death (voiced by Miguel Ferrer) appears to Simon in a vision, offering his one and only chance of escaping the curse of the crown.

Later, he recounts the events to a captured Muscle Princess, while Betty—who survived the struggle with Bella Noche—watches sadly from a window and flies off on the magic carpet.

[9] This pitch was submitted as an outline to the show's writers, who in turn worked with Moynihan and rewrote it to produce the final episode.

[10] Moynihan had originally wanted "Betty" to be a double episode so as to fit in all of the relevant plot information in a timely manner.

[6] Dunham and Adventure Time head writer Kent Osborne were Facebook friends, and knew each other from the independent film scene.

[14][15] Huntress Wizard, a character popular with the Adventure Time fanbase, was originally supposed to be featured in the episode.

Club awarded it an "A" and called it a "huge episode for the Ice King", because it marked "a major shift in the character's future by reconnecting with his past lover", Betty.

[20] He also applauded the casting of Dunham as Betty, noting that she "finds the emotional truth underneath the absurd situation to balance the drama and comedy of the script.