Another plot could involve Fem Batman and Joker in a sort of cat - and - mouse game where the Joker is specifically targeting Fem Batman because she's a woman. He might underestimate her at first, but she proves to be just as formidable as the male version. This would explore themes of gender and power in the Batman - Joker dynamic.
A plot could involve the reader having a special ability that both Batman and the Joker are interested in. Batman wants to use it for the good of Gotham, while the Joker wants to corrupt it for his own amusement. The reader has to navigate between these two very different forces, and in the process, discovers more about themselves and the nature of good and evil in Gotham.
Perhaps in the fanfiction, the Female Joker creates a series of mind - bending illusions across Gotham. Batman has to navigate through these illusions to find the real her and stop her from causing more chaos. Along the way, he starts to question his own sanity as the Female Joker's games get more and more intense.
A plot where they are friends in a post - apocalyptic Gotham is really engaging. In this world, they have to work together to survive against new threats like mutant gangs. Batman tries to bring some order while the Joker brings his unique brand of survival skills. Their friendship is tested as they have to deal with limited resources and moral dilemmas.
Well, sometimes in such fanfiction, there are alternate universes. For example, a world where the Joker and Batman have to team up against a greater evil. This flips their typical dynamic on its head and makes for an exciting read.
One interesting story could be where Joker tries to turn Gotham against Batman in a very psychological way in the fanfiction. He spreads rumors and false evidence to make the citizens doubt Batman's motives.
Some fanfictions might focus on the psychological aspects of their relationship. The Joker's insanity and Batman's unwavering sense of justice create a really unique dynamic. In slash fanfiction, this could be explored in terms of how they understand each other on a deeper level, perhaps a level that no one else can fathom.
One interesting story could be where Joker captures Batman and tries to break his spirit by showing him a distorted Gotham City that he has created in an abandoned area. Joker might use his henchmen to taunt Batman while he's trapped, but Batman uses his wits to find a way out and turn the situation around on Joker.
One interesting storyline could be Joker devising a new, elaborate plan to take over Gotham City that involves some wacky and unique traps. Batman, of course, has to use his Lego - themed gadgets and skills to stop him. Another could be a story where Joker and Batman are forced to team up against a greater threat, like a powerful alien invasion in the Lego universe. Maybe they start to understand each other a little better during this time.
One idea could be exploring a world where Batman and Joker have to team up against a greater evil. Maybe a powerful alien force arrives in Gotham and they realize they need to combine their skills, even if reluctantly.
One interesting plot could be the Joker and Harley trying to raise their baby in a world that is constantly against them. Maybe they have to protect the baby from other villains who want to use it for their own gains.