A really interesting plot could be a character who is reborn with memories of a different timeline. They use this knowledge to try and prevent a great disaster that they remember happening in the previous timeline. This would involve complex relationships with other characters who may not believe their warnings at first.
Well, a great plot might be that the OC has a unique magical ability related to memories. They can enter Severus Snape's memories and rewrite the painful ones. As they do this, Severus starts to change and become a more positive force in the wizarding world earlier. Also, the OC could be from a different magical culture and introduce Severus to new spells and ways of thinking that he can use to his advantage. This could lead to him having different relationships with the other characters like Dumbledore or Voldemort.
One idea could be an OC with a unique ki ability that no one in the Dragon Ball Z universe has seen before. For example, the ability to transform into an energy form that can pass through solid objects. Another plot could involve an OC who is from a long - lost race in the Dragon Ball Z lore and has to find their place among the Saiyans, Namekians, etc. A third idea might be an OC who is a time - traveler and has to prevent a major catastrophe in the Dragon Ball Z timeline.
You could insert yourself as a human knight. Picture this: you are part of the Stormwind army, and you get involved in the fight against the orcs. During a battle, you find a mysterious artifact that gives you special abilities. This leads you on a quest to find out more about the artifact's origin and how it can be used to save humanity from various threats like the Scourge or the demons.
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.