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.
There's a fanfiction that focuses on Finn's journey to save a vampire - infested kingdom. In this story, Finn teams up with some unlikely allies, including a vampire who has a change of heart. It shows Finn's determination and his ability to see the good in everyone, even vampires. The fanfiction is really detailed in terms of world - building, creating a whole new vampire - related ecosystem within the Adventure Time universe.
I'm not sure who the absolute best is, but some popular ones might be those who have a deep understanding of the Adventure Time universe. Writers who can capture Finn's adventurous spirit and Bear's unique personality well are usually great. For example, some authors on big fanfiction platforms who have a lot of positive reviews for their Adventure Time related works could be considered good authors.
I'm not sure who the 'best' is exactly, but there are many talented writers out there. Some popular ones might be those who have been writing in the Adventure Time fanfiction community for a long time and have a large following. They usually have a good understanding of the characters of Finn and the Fire Princess and can create engaging stories.
One aspect of 'Adventure Time Finn Alone Fanfiction' could be exploring Finn's character development in isolation. Finn is usually a very social character in the main series, so seeing him alone can show a different side of his personality, like his self - reliance and how he copes with solitude.
In some Adventure Time fanfictions, Finn might be betrayed by a character he trusted deeply, like Jake. For example, Jake could make a deal that goes against Finn's values in order to protect the Candy Kingdom, leaving Finn feeling betrayed as he sees it as a moral compromise. Another instance could be a new character in the fanfiction who befriends Finn only to steal his magic sword for their own gain.
One idea could be that Finn is kidnapped by an old enemy who wants to use him as a bargaining chip against Princess Bubblegum. Maybe they demand her to give up the Candy Kingdom in exchange for Finn's safe return.
One possible scenario in this fanfiction could be that Finn's transformation into a vampire brings out a whole new side of his personality. He might struggle with his newfound thirst for blood while still trying to uphold his heroic values. Maybe he teams up with Marceline, who is already a vampire, and she teaches him how to control his urges.
The Fire Kingdom's Flame Princess could be an ally too. Her mastery over fire could complement Finn's powers in combat situations. Also, the various magical creatures in Ooo, like the gnomes or the fairies, could band together and support Finn. They might have their own ancient knowledge or magic that could be useful to Finn in his adventures with his godlike powers. Finn's kindness towards them in the past might make them more inclined to help him out.
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.