One idea could be exploring the clone's struggle with identity. Is it doomed to be evil like the Joker or can it break free? Maybe it starts to have glimmers of goodness when it interacts with the Young Justice team.
A really cool idea would be if the Joker clone has memories implanted in it that are not its own. These false memories could make it believe it has a different origin or mission. The Young Justice team could then help it uncover the truth, leading to a journey of self - discovery and a possible alliance with the heroes.
Another interesting plot could be the clone being used as a weapon by a secret organization against the heroes. But as it gets closer to the Young Justice members, it begins to question its purpose. It could lead to a lot of internal conflict and interesting character development.
One idea could be exploring the clone's struggle to find its own identity apart from Black Canary. It might start off believing it has to be exactly like her but then discovers unique qualities within itself.
One idea could be a story where Ace teams up with Supergirl against the Joker's evil schemes in the Young Justice universe. Maybe Ace has some special abilities that complement Supergirl's powers.
A more complex plot could involve Ace having a hidden connection to the Joker that is slowly revealed. For example, Ace could be an experiment of the Joker's from the past that has now joined Young Justice, and the story could explore how this connection affects both Ace and the team.
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.
By having the clone interact with the Young Justice team, who have a strong sense of right and wrong. Their influence could make the clone reevaluate its own actions. For example, if it sees how they protect the innocent, it might start to wonder if its actions are justifiable.
One idea could be to create an OC who is a former victim of the Joker's madness and now has powers as a result. They could join the Young Justice team to seek revenge against the Joker. Another idea is an OC who is related to an existing character in the Young Justice universe and is lured into the Joker's chaotic world. For example, a relative of Robin who the Joker tries to corrupt.
The Flash clone in the fanfiction might have a different origin story compared to the original Flash. It could be the result of a scientific experiment gone wrong or a plot by a villain. This would add an element of mystery to the story.
One great 'Young Justice Joker Fanfiction' is 'Joker's Gambit'. It shows an interesting take on how the Joker might interact with the Young Justice team. The story is full of suspense and the characterizations are really well - done.
Maybe a story where some of the younger members of the Young Justice team are frustrated with the Justice League's methods and decide to take on a mission on their own, but end up getting in over their heads and have to call in the League for help. This could lead to a lot of character development and some interesting dynamics between the two groups.
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.