Another plotline might be that Finn is somehow separated from his friends and ends up on an island. There, he has to build a shelter, find food, and try to figure out how to get back to his friends. He could also meet new characters on the island who either help or hinder his journey.
Perhaps Finn is alone in a dream - like realm. He realizes that he can't wake up and has to navigate this strange world on his own. In this realm, the rules of reality are different, and he has to adapt quickly to survive and find a way out.
A possible plotline could be Finn getting lost in a magical forest all by himself. He has to find his way out while facing strange creatures and magical obstacles.
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.
Perhaps Finn's death is an accident. He could be exploring an uncharted area of Ooo and stumble upon a dangerous trap or ancient magic that he doesn't understand. His death shocks everyone in Ooo, and his friends start to question the safety of their continued adventures. This could lead to a whole new set of adventures for his friends as they try to come to terms with his death and make Ooo a safer place in his memory.
Another possible theme is the exploration of different cultures within the Adventure Time universe. Lady Rainicorn comes from a different species, and fanfictions can delve into how her culture and Finn's human - like culture interact and influence each other.
He could cry due to unrequited love. Finn has had his fair share of romantic interests in the show. In a fanfic, if the girl he loves doesn't return his feelings, it would be a heart - breaking situation for him. Also, in some fanfics, Finn might be confronted with the harsh reality of the world he lives in. Maybe he discovers something truly dark about the Land of Ooo that shatters his innocent view of it, causing him to break down in tears.
One possible storyline could be Finn exploring the world as Fionna. He might have to deal with the different social dynamics in the female - dominated version of the Adventure Time world. Maybe he'll struggle to fit in at first but then find his own place among the characters like Cake and Prince Gumball.
A plotline might involve their friends' reactions. After the kiss, Jake might be really surprised and have to adjust to the idea of his best friend being with Marceline. Princess Bubblegum could also have a reaction, perhaps being a bit jealous if she has some unspoken feelings for Finn. And there could be a plot where Finn and Marceline have to keep their relationship a secret at first because they're not sure how everyone will react.
A plotline might involve the amulet being a key to a hidden realm within the Nightosphere. The characters could go on a journey to find the amulet and then use it to enter this realm, where they face new challenges and meet strange creatures. It could also be that the amulet has the power to change the nature of the Nightosphere, and an evil character is trying to use it for their own dark purposes, so the heroes must stop them.
One possible plotline could be Marceline dealing with the challenges of pregnancy while still having to face the usual threats in the Land of Ooo. Maybe she has to rely on her friends like Finn and Jake more than ever for protection. Another could be exploring the relationship between her and the father of the baby, whoever that might be in the fanfiction, and how they navigate this new chapter in their lives.
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.