Maybe an OC who isn't really into racing but has to enter the races to save their friend who has been trapped in a glitchy part of the track. This OC could be really good at solving puzzles and uses that skill to navigate the dangerous parts of the Sugar Rush courses.
An OC that comes from a different part of the Sugar Rush world, a place that no one really knows about. They bring a new type of candy ingredient to the racing world which changes the rules of the game a bit. For example, their candy gives karts the ability to fly over certain obstacles for a short time.
One idea could be exploring the backstories of the side characters in more detail. For example, the neighbors or the people in the town where the main events take place. Another could be a 'what if' scenario, like what if Satou had made different choices earlier in the story.
Perhaps in a fantasy world, a rich lord takes Merlin as his 'sugar baby' not realizing Merlin's true potential as a powerful wizard. As time goes on, Merlin uses his influence over the lord to bring about positive changes in the kingdom, like improving the living conditions of the poor. This could lead to a complex relationship where the lord slowly discovers Merlin's magic and they have to deal with the consequences.
Another plot could revolve around an OC who is a Spartan trainee that doesn't quite fit the mold. They have a different way of thinking and approaching combat. In Halo 4, they end up being the key to solving a mystery related to the Prometheans. Maybe they find a way to communicate with the Prometheans and convince some of them to stop fighting the humans.
One idea could be an Otsutsuki OC who comes to Earth not for conquest but to study the unique life forms here. They could befriend some of the local ninjas and learn about the concept of friendship, which is alien to the Otsutsuki. This would lead to a series of adventures where they have to protect their new friends from other more hostile Otsutsuki members.
One idea could be an OC who is a long - lost relative of Moana. This OC could have been separated from the family during a great storm years ago. They could have unique skills, like being able to communicate with a different type of sea creature that Moana has never encountered. This would bring new adventures as Moana and the OC try to figure out how this new discovery could help their island.
One idea could be exploring the origin of the OC in the covenant world. Maybe they have a special power that sets them apart from the regular covenant members.
One idea could be an OC who is a new Wolfblood in a pack and has to prove themselves. Maybe they have a unique power that the others don't have and they have to learn how to control it while fitting into the pack's hierarchy.
One idea could be an OC who is a long - lost relative of one of the main characters. They suddenly show up and cause a stir in the power dynamics. For example, if they are related to the main heir, they might have a claim to the inheritance as well, leading to all kinds of family drama and power struggles.
One idea could be an OC who is a brilliant but unorthodox medical student. They constantly clash with House in their diagnostic methods yet prove to be surprisingly accurate at times. For example, they might use a new technology or approach that House is initially skeptical about but later comes to respect.
One idea could be an OC with the power to manipulate time joining the Incredibles. They could use their power to prevent disasters or even go back in time to change events that led to Syndrome's rise. Another idea is an OC who is a super - fast healer. They could play a crucial role in patching up the Incredibles after tough battles.