I highly recommend 'Partners in Crime'. In this fanfic, Harley and Ivy team up to take on some new villains in Gotham. It's full of action and at the same time, shows their relationship evolving. Another one is 'Under the Stars'. It has a more romantic tone as they go on a camping trip together, away from the city lights, and discover new aspects of their relationship while enjoying the beauty of nature.
Character development is key. Harley's journey from being Joker's sidekick to finding her own identity with Ivy by her side. And Ivy's growth as a character, her connection to nature and how that affects her relationship with Harley. Also, a unique plot. Maybe something like they go on a quest to save a part of Gotham's nature that's being destroyed, which ties in with Ivy's character. It should also have good dialogue that reflects their personalities, like Harley's crazy but endearing one - liners and Ivy's more serious, nature - centric statements.
One way to find the best authors is to look at the reviews and ratings of the fanfictions. Authors who consistently get high ratings and positive reviews are likely to be good at what they do. Also, some fanfiction platforms have recommended authors or popular stories sections. Checking those out can lead you to some great Harley Quinn and Ivy fanfiction authors.
One popular Harley Quinn and Ivy fanfiction story could be about their adventures in Gotham City after teaming up to take on a new villain. They use their unique skills and their deep bond to outwit the bad guy.
Harley's character could develop in many ways. She might become more protective and motherly, which is a big change from her usually wild and carefree self. This new - found sense of responsibility could make her question her relationship with Joker and the life of crime they lead.
Love triangles are quite common. There could be a love triangle between Batman, Harley Quinn, and Poison Ivy. Sometimes Harley might be caught between her old feelings for the Joker and new feelings for Batman or someone else. The theme of female empowerment is also prevalent. Fanfics often showcase Poison Ivy's strong connection to nature and her ability to use it as a force, and Harley Quinn's growth from a sidekick - like figure to a more independent character.
Friendship is another big theme. Despite their different personalities, they form a bond. In some fanfics, they start out as rivals but gradually become friends. Their friendship is shown as something that makes them stronger. For instance, they might help each other out of tough situations like escaping from Arkham Asylum.
A common theme is friendship. Their unique bond, whether it's a platonic or a more romantic - leaning one, is often explored. It shows how they support each other through Gotham's chaos.