He might find himself more in tune with the natural world of Gotham. As a bat, he could discover new secrets about the city's underground and hidden places that he never knew before. This could lead to him uncovering a whole new level of crime and corruption in Gotham that was previously hidden from his human eyes.
Maybe his relationship with his rogues gallery changes. For example, the Penguin, who has an affinity for birds and animals, might see Batman's transformation as an opportunity to either befriend him or use him for his own evil purposes. Batman would have to navigate this new dynamic while also dealing with his own altered state.
Another possibility is that Batman is experimenting with a new technology to enhance his abilities. He creates a device that is supposed to give him the ability to fly like a bat. However, something goes wrong during the testing phase. The device fuses with his DNA, and he starts to turn into a bat. He has to deal with the physical and mental changes, all while trying to keep it a secret from his allies like Alfred and Commissioner Gordon.
Well, he might find it really hard to operate his Bat - gadgets as a cat. His paws are not made for pushing buttons or typing on keyboards. So he has to figure out a way to adapt. Maybe he uses his cat claws to scratch out messages for Alfred to understand what he wants to do.
Perhaps it's due to a psychological breakdown. Batman has endured so much trauma over the years. The constant fight against crime, the loss of loved ones, and the never - ending battle with his inner demons could all take a toll. One day, he just snaps. His mind can no longer handle the pressure, and in an attempt to escape from his own tortured self, he subconsciously adopts the persona of the Joker, as the Joker seems to have no such moral and emotional burdens.
Well, in this kind of fanfiction, perhaps the Bat - family would be in a total chaos. Alfred would suddenly have to take care of a baby Batman. He'd have to change diapers, feed him, and keep him out of trouble. Robin might be really confused at first but then would probably take on a protective role like a big brother.
The superheroine's enemies might see this as an opportunity to finally get rid of her for good. They could try to kidnap the baby - superheroine. But her allies would be on high alert and do everything to protect her. For instance, they could set up a secret hideout where they keep her safe while researching a solution.
Well, her powers would be gone or at least dormant as a baby. So she'd be completely defenseless. Her friends would have to protect her from all the villains who might see this as an opportunity to get rid of her. For example, Lex Luthor could try to kidnap her. But her friends like Jimmy Olsen would do everything they can to keep her safe.
In this fanfiction, Batman could encounter a new inmate who has powers or knowledge that could help him escape. However, this inmate has his own agenda. Batman has to figure out how to work with this person without getting double - crossed. Also, the asylum could be a place where some dark secrets of Gotham are hidden. Batman's presence there could trigger the revelation of these secrets, which in turn could change the power dynamics in the city once he gets out.
The Joker might try to make Batman laugh at his own jokes as a form of humiliation. He could use his trademark laughing gas in a way that forces Batman to either laugh or suffocate.
Well, maybe Gordon finally gets to understand the Bat family's true identities. He could be shocked at first, but then start to work even more closely with them.
One interesting scenario in this fanfiction could be the cultural clash. The Avengers are more used to big - scale, world - saving operations often involving aliens and super - science. The Bat family, on the other hand, is deeply rooted in the dark alleys of Gotham, dealing with more down - to - earth criminals. This contrast could lead to some humorous misunderstandings at first, like Captain America being shocked at Batman's more 'vigilante' methods, but eventually they could learn from each other.