Another idea is a crossover with the Ghostbusters. Batman might initially be skeptical of the Ghostbusters' methods, but they could prove useful when Gotham is haunted by some supernatural forces. The contrast between Batman's dark and brooding nature and the Ghostbusters' more comical approach would make for an entertaining story.
One idea could be a crossover with the Teenage Mutant Ninja Turtles. Batman could team up with the turtles to take on a common enemy like the Shredder and the Joker working together. They could combine their unique fighting styles and gadgets to outwit the villains.
A crossover with the Justice League Animated Series would also be cool. Imagine Batman from 'Batman the Animated Series' interacting with different versions of his fellow Justice League members. There could be some interesting dynamics as they deal with a threat that requires both his detective skills and their superpowers.
One interesting crossover idea could be Naruto visiting Gotham City. He'd be shocked by the dark and gritty environment compared to his own village. His ninja skills could help Batman in fighting villains in unexpected ways, like using his shadow clones to create distractions during a heist. Another idea is Batman somehow ending up in the Naruto world and learning about chakra. He could use his detective skills to figure out how to use it in his own unique way.
An interesting idea is to write a story where Catwoman discovers a secret about Batman's past that even he doesn't know. This could lead to a strange alliance between them as they both try to figure out what the discovery means. It would also add a new layer to their relationship.
One idea could be creating an original character (OC) who is a new villain in Gotham. This OC could have a unique power, like the ability to control technology. They would target Batman's high - tech gadgets and try to disrupt his crime - fighting efforts.
One interesting concept could be exploring Batman's early days as a vigilante in fanfiction. Writers might show his struggles with learning to fight crime effectively while also dealing with his own inner demons.
Another interesting concept is to have a character crossover. For example, Bumblebee from the Animated series could somehow end up in the world of the live - action Transformers movies. His small and agile form might be a big contrast to the more bulky Transformers in the movies. He could form an unexpected friendship with a human character, like Sam Witwicky, and together they could help the Autobots in the movieverse with a mission that requires his speed and intelligence.
One idea could be a fanfiction where Poison Ivy teams up with another villain, like the Joker. They could have a really strange alliance. Maybe she uses her plant powers to help him with one of his crazy schemes, but in the end, she double - crosses him because she realizes his plans are too chaotic even for her. It would be an interesting exploration of her character and how she interacts with other villains in the Batman universe.
One idea could be that Batman finds himself in the Marvel universe due to a strange multiverse rift. He teams up with Iron Man to stop a tech - based villain who is stealing advanced technology from both their worlds. Another could be Batman and Spider - Man working together in Gotham. Spider - Man's acrobatics and sense would be a great addition to Batman's detective skills.
One idea could be Batman coming to Star City to help Arrow deal with a new, extremely dangerous criminal organization that has ties to Gotham. This could lead to some great fight scenes as they combine their skills and resources.
A cool batman crossover fanfic idea might involve a crossover with the Avengers. Batman's strategic mind and detective abilities would be a great addition to the superhero team. He could help Iron Man with tech, or use his stealth to outwit Loki. Also, a crossover with the Doctor from Doctor Who could be fascinating. Batman could travel through time and space with the Doctor, solving mysteries in different eras.
One idea could be that the Flash has to help Batman track down a super - villain who has the ability to manipulate time. Since the Flash is a speedster, he can move through time - altered situations more easily. Another plot could involve Batman creating a new gadget to counter a meta - human threat, and the Flash accidentally gets caught in its test run, causing some wacky time - space anomalies that they have to work together to fix.