A cool plot could be that Alice has special powers in this fanfic. She can communicate with the souls of the fallen humans in a way that no one else can. This ability leads her on a quest to find out the true history of the Underground and how to break the cycle of human - monster conflict.
One idea could be that Alice finds herself in the Underground and has to navigate through the different areas using her unique sense of wonder. Maybe she befriends some of the monsters like Toriel and they go on an adventure together to find a way out for her.
One idea could be that the animatronics from FNAF end up in the Undertale universe. They might be mistaken for strange monsters at first. The Sans character could be particularly intrigued by their mechanical nature and try to figure out how they work.
Another plot idea is a story where the antagonists from both games, such as Flowey from Undertale and the King from Deltarune, form an alliance. Their goal could be to take over both universes. This would force the heroes of both games to work together. The fanfic could explore how the different characters with their own powers and personalities interact and strategize to defeat this powerful alliance.
One idea could be that the characters from Homestuck end up in the Underground of Undertale. They might have to deal with the various monsters there while also trying to find a way back home. Maybe John Egbert could team up with Frisk and they use their unique abilities to overcome challenges like puzzles and battles.
One idea could be that Alice returns to Wonderland as an adult and has to deal with new, more complex riddles and challenges that are related to the grown - up world she now knows. For example, the Queen of Hearts might be having a 'tax collection' problem in her kingdom and Alice has to use her real - world knowledge of economics to solve it.
Another plot could involve new characters being introduced into the Borderland. These new characters could have unique abilities or knowledge that either helps or hinders the main characters in their struggle to survive. Maybe they know a secret about the origin of the Borderland that could change everything.
One idea could be exploring how the other characters in the Bendy universe react to the news. For example, the more mischievous characters might be curious and cause some light - hearted chaos. Another plot could involve Bendy and Alice preparing for the arrival of their baby, like building a nursery in their spooky yet charming world.
Your OC could be a transfer student from a far - off place with a different understanding of Alices. They might struggle to fit in at first but then use their unique perspective to solve a big problem at the school. For example, if there's a conflict between different groups of students with different Alices, the OC could find a way to bring them together through their outsider view.
One idea could be exploring an alternate timeline where Sans and Papyrus have different roles. For example, Papyrus could be the more serious and powerful one while Sans is more carefree. Another idea is to write a fanfic centered around a new character who gets trapped in the Underground and has to navigate through the various regions, making unique friendships along the way. And a third idea could be a fanfic that focuses on the backstory of the monsters before they were trapped underground, showing how their society was and how it changed over time.
Here are some plot ideas. First, the adult human could be a scientist. They meet Toriel and start to analyze the magic in the Underground. As they collaborate, they grow closer. Second, the human might be a storyteller. They tell Toriel tales of great heroes and adventures from the surface. Toriel is so captivated that she wants to be part of those stories with the human. Third, the human has a troubled past. Toriel, with her motherly nature, helps the human heal. Through this process, their relationship blossoms. In all these ideas, their relationship can develop in a non - sexual, deep and meaningful way, exploring themes of friendship, understanding and hope.
Perhaps the Alice boy forms an unlikely alliance with some of the more mischievous characters in Wonderland. They could team up to outwit a powerful and tyrannical new villain that has emerged in the land. He uses his unique perspective as an outsider to come up with creative solutions to the problems they face.