One idea could be that PB accidentally creates a magical device that swaps their personalities. Marceline then has to deal with being super sweet and girly while PB tries to maintain her tough rocker image. It would lead to a lot of comical situations as they try to navigate their daily lives in each other's shoes.
Their relationship could be developed through music. Marceline could teach PB how to play the guitar, and in the process, they open up to each other about their past traumas. PB might share her insecurities about ruling the Candy Kingdom, and Marceline could talk about her loneliness as a vampire.
One great 'Adventure Time PB and Finn Fanfiction' is 'The Unlikely Bond'. It beautifully explores the friendship between PB and Finn in a new adventure where they have to solve a mystery in the Candy Kingdom. The story is full of the charm and humor that the show is known for.
The plot needs to be engaging. It could be a new adventure in Ooo, like exploring an uncharted part of the Land of Ooo or dealing with a new magical problem. It also helps if there are some emotional elements, like a conflict between PB and Finn that they have to resolve, which deepens their relationship.
The writing style matters a great deal. A great Marceline x PB fanfic uses vivid descriptions to bring the characters and their world to life. It might describe Marceline's cool, edgy style and Princess Bubblegum's scientific - mindedness in a way that makes the readers feel like they are right there in the Land of Ooo with them.
Yes, there might be some. Fanfiction websites like Archive of Our Own (AO3) could potentially have such fanfictions. However, the availability may vary. Some fanfic writers might explore this idea as a creative concept within the Adventure Time universe, but it's important to note that fanfiction is a form of fan - created content and not part of the official canon.
One popular theme is friendship exploration. Since PB and Marceline have a complex relationship in the original work, fanfictions often delve deeper into how their friendship could develop in different scenarios.
You can try websites like Archive of Our Own (AO3). It has a large collection of fanfictions. Just search for 'pb x marceline' there, and you'll likely find many interesting stories.
A good Adventure Time Marceline fanfiction often has a strong understanding of her character. It should capture her edgy, yet vulnerable side. For example, her relationship with her past and her father is a great aspect to explore.