In fanfiction, the Winged OC can be a protector of a special place in the TMNT universe. For example, a sacred garden on a rooftop that has magical plants. The TMNT discover this place and the Winged OC warns them about the dangers of disturbing it. But as they get to know each other, they find common ground in protecting the city from bigger threats, and the Winged OC becomes a valuable part of the TMNT's network of allies.
A Winged OC can fit in as a new ally. For instance, if the TMNT are facing a foe that has an aerial advantage, the Winged OC can use their flight abilities to even the odds. They could also be a source of new knowledge, like knowledge about a hidden part of the city that can only be reached by flying.
A Dragonborn OC can fit into the RWBY universe by having their own unique backstory related to dragons. For example, they could have been born in a world where dragons were both feared and revered. When they enter the RWBY universe, their dragon - like abilities such as enhanced speed, strength, and the ability to breathe fire or ice can make them stand out. They could become a new type of huntsman or huntress, using their powers for good.
One idea could be a Winged OC who is from a different dimension and has the power to heal. The OC could encounter the TMNT during a battle where one of them is seriously injured. Another plot could be that the Winged OC is on a quest to find a lost artifact, and the TMNT get involved either by accident or because they also have an interest in the artifact. Or perhaps the Winged OC is a runaway from an evil organization that the TMNT are trying to take down, and they form an alliance.
An 'oc' can fit into the Disney universe by having a backstory that ties into the existing lore. For instance, if it's a 'Beauty and the Beast' fanfiction, the 'oc' could be from a neighboring village that has always had a strange connection to the enchanted castle. This connection can be explored through interactions with Belle and the Beast.
In terms of power levels, the Immortal Mage could have powers that are on par with the likes of Scarlet Witch or Doctor Strange. Their immortality might also come with the ability to regenerate from any injury, making them a formidable force. They could also have the power to travel through different dimensions, which is a common theme in Marvel. This would allow them to access hidden knowledge and artifacts that could be used to either protect or disrupt the Marvel Universe depending on their motives.
Appearance - wise, the male OC could have a look that blends in with the Feudal Japan setting. Maybe long hair tied back, wearing traditional robes. His personality should also match the era's values to some extent. For example, he could be honorable and brave, but also have a bit of a stubborn streak. This would make him fit in with the other characters like Inuyasha who also have strong personalities.
A half - Grimm OC could fit in as an outcast. Since Grimm are the enemies in the RWBY universe, a half - Grimm would be seen with suspicion. But they could also be a key to understanding the Grimm better. For instance, they might be able to detect hidden Grimm lairs or weaknesses that others can't. They could team up with the main characters like Ruby and the others, gradually earning their trust through their unique skills.
The OC should have a unique backstory that ties into the existing Avengers lore. For example, if the OC has powers, their origin could be related to an event in the Marvel universe. Also, their personality should complement the Avengers. If they're too similar to Steve Rogers, it might be boring. So, they could be more carefree while Steve is more serious. And they should have a clear motivation, like wanting to protect the world or seeking revenge for a past wrong, that aligns with the Avengers' overall goals.
An oc can take care of the TMNT in fanfiction by providing them with a safe place to stay. Maybe the oc has a hidden base or a well - protected home where the TMNT can rest and recover from their battles.
The OC could be a new hero from a different part of the world. For example, if they come from a small, technologically advanced country, they could bring a fresh perspective to the Marvel universe. Their skills and abilities could complement Spider - Man and Iron Man. They might start by helping out in local problems in their home country and then get noticed by the two heroes, eventually joining them in bigger battles.
The OC, as the Son of Sparda, could fit in by being a new and powerful entity. He might be initially seen as an outsider, but his powers would quickly draw attention. He could become involved in the power struggles between the different factions in Highschool DxD. For example, the devils might try to recruit him, while the angels might be wary of his presence. His unique abilities would also make him a valuable ally or a fearsome opponent. And in the high school setting, he could be a bit of an enigma to the other students, both human and supernatural.