A fanfiction could also focus on the relationships between the characters. In the Injustice world, relationships are often strained due to the extreme circumstances. The Young Justice characters could bring a fresh perspective on friendship and loyalty. For instance, Robin could team up with Nightwing from the Injustice universe and they could share their different experiences and strategies, which could help them both grow as characters and also have an impact on the overall plot as they work together to fight against the tyranny in the Injustice world.
One idea could be exploring how the Young Justice team would react to the dystopian world of Injustice. For example, they might try to find a way to restore justice and balance without using the extreme methods seen in the Injustice universe. Maybe they would focus on rehabilitating the villains instead of just punishing them.
Another interesting angle could be a crossover of characters. Imagine Superboy from Young Justice meeting an alternate version of Superman from Injustice. They could have a deep conversation about power and responsibility, with Superboy trying to convince the other Superman that there are better ways to deal with the situation. This could lead to a series of events where the Young Justice team starts to influence the Injustice world in a positive way.
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 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.
I think Superboy would be really interesting. In Young Justice, he's still finding his place and dealing with his Kryptonian powers. In the Injustice universe, he'd be faced with a very different version of Superman. He could be a bridge between the two worlds, trying to understand the darker side of power that the Injustice Superman has embraced while also holding onto his own ideals from Young Justice.
Some fanfictions focus on the relationships between characters in the Young Justice Injustice scenario. Such as how friendships are strained or strengthened when faced with the moral dilemmas that the Injustice concept brings to the Young Justice universe.
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.
One idea could be that Ghost Rider somehow gets transported into the Young Justice universe. He might initially be seen as a threat by the team. But then they realize he's fighting against a common evil that has ties to the dark forces in both their worlds. For example, a demon that is trying to open a portal to bring more chaos.
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.
One idea could be a crossover where the Young Justice team has to team up with the Justice League to face an interdimensional threat. Maybe a powerful villain from another dimension is trying to invade Earth and the combined skills and powers of both groups are needed to stop it.