Well, if an OC is stuck in a Supernatural fanfiction, it could end up joining the Winchester brothers on their hunts. Maybe they have some unique ability that could help Sam and Dean. Or they could get into trouble trying to use modern knowledge in a world full of magic and the unknown. They might introduce new ideas about how to deal with the supernatural, which could either be a great help or cause chaos.
First of all, the OC would be in a world full of danger. The Supernatural universe has its own set of rules and powers. The OC might struggle to understand these rules at first. They could befriend some of the characters from the original story, like Castiel. This friendship could lead to the OC getting involved in the ongoing battles between good and evil in the fanfiction world. They may also have to deal with their own identity crisis as they are not from that world, but are now a part of it and have to figure out their role.
Well, perhaps in 'pooh gets stuck crossover fanfiction', Pooh gets stuck while trying to follow a new friend from the crossover world. Say it's a crossover with a sci - fi world and he's following an alien through some sort of energy portal, but then the portal malfunctions and he's left stuck in a weird in - between space.
They might encounter advanced Pokémon species that don't exist in their time. For example, new evolutions or completely new types of Pokémon. This could lead to new adventures and challenges as they try to understand and befriend these Pokémon.
He might have to face challenges that are different from those in the wizarding world. For example, the rules of the game could be strange and he'd need to figure them out quickly. Maybe he'd encounter characters from other fictional universes or versions of his friends with altered personalities.
Another thing that could occur is that they encounter some strange creatures or phenomena inside the box. Naruto would be ready to fight, but Hinata might first try to understand the nature of these things. They'd have to combine their different approaches to deal with the situation, and in the process, their relationship would evolve, whether it's becoming better friends or something more romantic.
In this fanfiction situation, they could end up using their knowledge of the future to help people in the past. For example, Ash could use his Pokémon training skills to solve some problems that people in the past were having with wild Pokémon. Serena could perhaps use her cooking skills to introduce new recipes. And together, they would be constantly looking for clues or a magical item that could send them back to their time.
One way might be to seek help from a powerful being in the Supernatural world, like a witch or an archangel. If they can convince this being to help them, they might be able to return home. Another option is to reverse whatever event brought them into the fanfiction world in the first place.
He might find himself in strange situations that the fanfiction writer has created. For example, he could be stuck in an alternate dimension where the rules of his powers are different. Maybe he's trapped in a world where all his friends have turned against him because of a plot twist in the fanfic.
Well, she could be rescued by her friends. Maybe Naruto would use his shadow clone jutsu to climb the tree and get her down.
They could use their ninja skills to try and break out of the box. Naruto might try his Rasengan, while Hinata could use her Gentle Fist to find weak points in the box's structure.
There's a chance that he'll meet some sort of magical creature that has made the cupboard its home. This could be a friendly creature that helps him get out or a more mischievous one that makes his situation even more difficult. He'll have to use his wits and magic skills to deal with it.