Maybe in the fanfiction, Sulley discovers that Randall has a hidden side. Randall might be secretly trying to protect the monsters from a new threat in the human world that no one else is aware of. Sulley initially doubts Randall but as he sees the evidence, he decides to help Randall. They then team up and use their different skills - Sulley's big and strong nature and Randall's sneaky and intelligent ways - to overcome the threat and in the process, their relationship changes for the better.
In a different take, Sulley and Randall could be partners in a secret experiment within Monsters Inc. They might be working on a new way to collect energy from kids without scaring them. As they work closely together, they discover that they have a lot in common when it comes to their love for the monster world and their hopes for its future. This shared passion could lead to a deeper bond between them, different from the adversarial relationship in the movie.
One good example could be fanfictions that focus on their adventures outside of work. For instance, a story where they go on a trip to a new, uncharted part of the monster world. Another might be ones that explore their friendship during their childhoods, like how they first met at monster school.
It's also because their personalities are so different yet complementary. Sulley is big and strong while Mike is small and smart. Fanfiction writers can play with these characteristics in various ways. For example, they can create stories where Mike's ideas and Sulley's ability to execute them lead to amazing results. This contrast makes for interesting and engaging stories.
Friendship is a very common theme. Since the OC is a new character, often the story focuses on how they become friends with Sulley. For example, they might help each other out in tricky situations at Monster Inc.
Monsters Inc. is set in a world where monsters generate energy from children's screams. But as the story progresses, we discover that laughter can generate even more powerful energy, leading to a major shift in the monsters' way of doing things.
One idea could be exploring the backstories of the monsters more deeply. For example, what was Sulley's life like as a young monster? Another could be a story where Boo somehow returns to the monster world as an adult. Or a fanfiction about the monsters having to deal with a new kind of energy source other than screams.
There's also a fanfic called 'Sulley and the Mysterious OC'. In this one, a mysterious OC shows up at Monster Inc and Sulley is the first to notice something strange about them. It has a lot of mystery elements and is quite engaging. It delves into the idea of how the monsters at Monster Inc react to an unknown entity in their midst.
Some well-known names include Sulley and Mike Wazowski. They are the main characters and very popular among fans.
There could be a fanfiction where a human scientist figures out a way to communicate with the monsters in Monstropolis. This scientist then tries to bridge the gap between the two worlds, leading to a series of events where both humans and monsters learn more about each other. For example, the scientist might introduce the concept of different human cultures to the monsters, which they find fascinating.
One idea could be a crossover with 'Toy Story'. The monsters could accidentally enter Andy's room and interact with the toys. It would be hilarious to see Sulley and Woody trying to understand each other's worlds.