Another idea is to create a story where the OC is trying to find a cure for Joker Venom. They could be a scientist or a vigilante with a personal vendetta against the chaos it causes. They might face many obstacles, like being hunted by Joker's henchmen or not being trusted by the authorities.
Focus on unique character design. Give your OC distinct physical features, a memorable backstory related to Joker Venom, and a personality that sets them apart from other characters in the Batman/Joker universe.
One great 'Joker Harley OC Fanfic' is 'Harley's Redemption'. It delves deep into the character of Harley Quinn as an original character in a new, exciting story. Another one could be 'Joker's New Toy', which has a unique take on the relationship between Joker and Harley. And 'The OC's Impact' shows how an original character can change the dynamic in the Gotham underworld.
One idea could be the daughter's struggle to come to terms with her father's villainous nature. She might try to break away from the Joker's influence and find her own path in Gotham, perhaps becoming a vigilante of sorts. Another could be a story where she is kidnapped by Batman's enemies to use as leverage against the Joker.
Well, in many 'joker x oc fanfic' works, the OC could be a psychiatrist who tries to understand the Joker. This creates an interesting dynamic as the OC is drawn into the Joker's mind games. Some fanfics also show the OC having some sort of special ability that either attracts or repels the Joker, leading to intense and often unpredictable interactions.
One possible scenario in an 'OC Becomes Venom' fanfiction could be that the OC is an ordinary person who stumbles upon the Venom symbiote. Maybe they're in a lab accident or find it in an alley. Once bonded, they start to struggle with the new powers and the alien's aggressive nature. At first, they might accidentally use the powers in ways that cause chaos, like breaking things when they try to move quickly. But as time goes on, they learn to control it and use it for good, like protecting their neighborhood from small - time criminals.
Definitely Harley Quinn. She has a complex relationship with the Joker and her interactions with his daughter could be very interesting. Also, Batman himself. His reaction to the existence of the Joker's daughter and how he might try to either protect or use her against the Joker would add depth to the story. And of course, Commissioner Gordon, who could represent the law and order side trying to deal with this new complication.
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.
Well, the plot could involve the Venom symbiote OC trying to protect a small town from a group of villains. Maybe there's a big bad corporation that's polluting the environment and the symbiote OC uses its powers to stop them. It could also form an unlikely alliance with some local heroes.
One common theme is the struggle for power. Often, the OC has to deal with the overwhelming power of Venom and either learn to control it or be controlled by it. For example, in some fanfics, the OC tries to use Venom's power for good but has to constantly battle the darker impulses that come with it.