One idea could be an OC with unique powers joining the Young Justice team. For example, an OC who can manipulate time in small increments. This would create interesting scenarios during battles and team strategizing.
One idea could be that the OC is a new meta - human with a unique power that Batman is initially suspicious of. Maybe the OC's power is related to mind - reading, and they accidentally read Batman's thoughts during a mission, leading to some tense and comical moments as Batman tries to keep his secrets while also using the OC's power to their advantage. Another plot could involve the OC being from a different dimension and Batman has to help them adapt to Earth - 16 (the Young Justice universe) while also dealing with the threat that the OC's arrival may have brought. Or perhaps the OC has a connection to an old enemy of Batman's, and they must work together to uncover the mystery behind it.
Another idea is that the OC is a non - magic user who gets caught in a magical conflict that Zatanna is involved in. The OC has to rely on their wits and physical skills while Zatanna uses her magic. Their relationship could grow as they learn from each other's strengths and weaknesses. For example, the OC might teach Zatanna some street - smart tactics, and Zatanna could introduce the OC to the world of magic.
A possible plot is that the OC is a new recruit to the Young Justice team. Miss Martian is assigned to train the OC. At first, they don't get along because the OC is headstrong and doesn't like taking orders. But as they face various challenges together, like fighting against a powerful enemy that targets the team's weaknesses, they start to understand each other better. The OC could also have a secret past that Miss Martian helps uncover, which deepens their bond.
One idea could be an OC with a unique power, like the ability to manipulate sound waves. They could join the Outsiders and use their power in unexpected ways during battles, for example, creating sonic illusions to confuse enemies. Another plot could involve an OC who is from a different dimension and has to adapt to the Young Justice Outsiders' world while also bringing some of their own world's knowledge and technology. Or perhaps an OC who has a personal vendetta against a villain that the Outsiders are also after, and they initially clash with the team but then learn to work together.
One idea could be that the OC has a unique power that the Justice League initially distrusts but later comes to rely on. For example, the OC can manipulate time in small bursts, which at first seems dangerous but is actually crucial in stopping a villain who can freeze time.
One plot idea could be that Venom somehow gets transported to the Young Justice universe and forms an uneasy alliance with the team. Maybe at first they see Venom as a threat but then realize his power can be used against a greater common enemy.
A possible plot could be a time - travel related one. A character from the Regeneration world accidentally travels to the Young Justice timeline and messes up some key events. Now the Young Justice team, along with the help of some friendly Regeneration characters, have to fix the timeline while also dealing with the consequences of the changes that have already occurred.
One idea could be that Naruto is somehow transported to the Young Justice universe. He then has to learn how to work with the team while also dealing with villains he's never faced before. Another plot could be that a villain uses some sort of magic or technology to merge the two worlds, forcing Naruto and the Young Justice members to cooperate to separate them again.
One idea could be an OC Green Lantern from a different planet arriving on Earth and having to adjust to the Young Justice team's way of doing things. They might have unique powers related to their home planet's culture that add new elements to the team's battles.
One idea could be that the male OC clone discovers he has unique powers not shared by the original he was cloned from. For example, he might be able to manipulate energy in a way that surprises everyone. Another plot could involve the clone trying to find his own identity separate from the expectations placed on him because of his origin. He could struggle with whether to follow in the footsteps of the original or forge his own path.