Maybe Harley Quinn discovers some dark secret about Nightwing's past that she uses to blackmail him into helping her with a heist. But as they work together, they start to understand each other better. Nightwing realizes Harley isn't all bad and Harley sees that Nightwing has his own demons. In the end, they might even become friends or something more.
Another plot could be set in an alternate universe where Harley Quinn and Nightwing are part of a resistance against an evil regime. Harley's chaotic nature and Nightwing's leadership skills combine to lead the charge. They have to overcome their differences and trust each other completely to succeed in their fight for freedom.
One idea could be a story where Harley Quinn tries to break free from the Joker's control completely and starts her own life of crime without him. She could form her own gang and prove that she's more than just the Joker's sidekick.
One idea could be that Harley Quinn and Deadpool team up to take on a common enemy who has been causing chaos in both their worlds. They could start off as reluctant partners, with Harley being annoyed by Deadpool's constant chatter and Deadpool finding Harley's craziness a bit much at first. But as they fight side by side, they learn to appreciate each other's skills and form an unlikely friendship.
One plot idea could be that Deadpool and Harley Quinn team up to take on a common enemy, like a new super - villain in Gotham who has a connection to some of Deadpool's foes. They could start off not getting along because of their different personalities, Deadpool's fourth - wall - breaking and Harley's chaotic - cute nature. But as they face challenges together, they learn to work as a team and even become friends.
One idea could be Harley Quinn trying to reform herself and Batman being reluctantly drawn into helping her. Maybe she has some crucial information about a new villain in Gotham and in exchange for her safety and a chance at a new life, she offers to work with Batman.
One idea could be that Harley Quinn tries to reform herself to be worthy of Batman's trust. Maybe she starts secretly helping Batman take down other villains in Gotham. Another could be a situation where they are forced to team up against a common, extremely powerful enemy, like a new supervillain who has a plan to destroy Gotham. And a third idea is that Harley Quinn has a change of heart about the Joker after seeing how Batman is constantly fighting for good, and she begins to see Batman in a new light, leading to a complex relationship between them.
One idea could be that they are both transported to an alternate dimension. In this dimension, all the rules are different. Deadpool's healing factor doesn't work as well, and Harley Quinn's usual weapons are useless. They have to rely on each other's skills and knowledge to find a way back home. Along the way, they meet strange versions of their friends and enemies, which adds to the hilarity and confusion.
One idea could be that Deadpool and Harley Quinn team up to take on a common enemy, like a supervillain who's causing chaos in Gotham and also has a connection to one of Deadpool's foes. They could start off bickering because of their very different personalities but gradually learn to work together.
One idea could be Harley Quinn traveling back in time to meet the Joker before he became the criminal he is. She could try to change his path, which would create a whole new set of events in the Gotham underworld. Another plot could involve her traveling to the future and seeing a Gotham where she has become a hero. She then has to figure out how to make that future a reality in her own time. And perhaps she travels through different time periods in Gotham's history, interacting with different versions of Batman and his rogues gallery.
One idea could be that the OC is a new villain in Gotham and Harley Quinn takes an immediate liking to their chaotic style. They team up to pull off a heist on one of Gotham's richest, with Harley's unpredictable nature and the OC's unique skills making for an exciting adventure.
One idea could be that Harley Quinn somehow ends up in the wizarding world. Maybe she mistakes Hogwarts for a really strange asylum at first. She could then start causing chaos with her wacky personality and unique fighting style, which would be a huge shock to the Hogwarts students and professors.