Well, one possibility could be that Danny gets hit by some sort of ghostly ray that de - ages him. His friends, Sam and Tucker, would then have to take care of him while trying to figure out how to reverse the effect. They might face challenges like hiding him from his parents, who would be really confused if they saw their teenage son turned into a toddler. Also, Danny's ghost powers could be all out of whack in his toddler form, causing some unexpected chaos around town.
One possible plot could be that Danny Phantom, while exploring some sort of interdimensional rift, gets zapped by a strange energy that transforms him into a Pokemon. Maybe he becomes a Pikachu. He then has to figure out how to use his new Pokemon abilities to get back to his normal form. He might start by trying to communicate with other Pokemon, learning their ways and using his ghostly knowledge to his advantage in the Pokemon world.
Well, one possible plot could be that Danny, while on an underwater mission to stop some ghostly threat near the ocean floor, gets hit by a strange spell or artifact that turns him into a mermaid. He then has to deal with his new form while also trying to keep his ghost - fighting duties going. Maybe he discovers new powers related to his mermaid form that help him in his battles.
Sam would probably be very protective. She'd be the one making sure Danny was fed and clean. Tucker would be more into trying to figure out how to fix the situation using his tech skills. They'd both be really shocked at first, but then quickly adapt to taking care of Danny. They might have to come up with excuses for Danny's parents about why he wasn't around or why he was acting so strange.
In this fanfiction, it could be that Danny Phantom meets a Danny Phantom from a parallel fan - made story. At first, they don't trust each other. But as they learn more about each other's worlds, they realize that there are some common elements that are being threatened. It could be that a powerful ghost is trying to rewrite all the fanfic universes related to Danny Phantom. So, they must combine their strengths and knowledge to stop this from happening.
Perhaps there could be a love interest that is unique to his female form. Maybe someone who didn't notice Danny before as a boy, but now is attracted to him as a girl. This could add a whole new layer of drama and romance to the fanfiction, as Danny has to figure out how to handle this new relationship while still dealing with his ghost - hunting duties.
The plot could involve some sort of mystery related to the pregnancy. Like, there could be a ghostly force that is either helping or hindering the pregnancy. And they have to figure out what it is and how to deal with it. Also, their friends like Tucker could play important roles in supporting them.
The plot could be centered around a mystery. A strange series of events start happening in Amity Park and it seems to be related to some new technology that Dr. Drakken has created. Danny Phantom investigates and runs into Shego. They start off as adversaries but as they dig deeper, they realize they need to work together to solve the mystery. Maybe there's a hidden force that is using Drakken's tech to open portals to the Ghost Zone and release dangerous ghosts, and only Danny and Shego can stop it.
Well, in the 'danny phantom is a lion fanfiction', it could be that Danny is cursed to become a lion at times. As a lion, he discovers new aspects of the ghost world. For example, there could be a group of lion - like ghosts that only communicate with him when he's in lion form, and they tell him secrets about his powers or his family's past that he didn't know before.
One possible plot could be that Izuku discovers the existence of Danny Phantom through some kind of interdimensional event. He then tries to learn from Danny's way of handling his powers and his secret identity, applying those lessons to his own journey as a hero in training.
One possibility is that Danny gets tired of constantly being the hero and facing so much pressure. He might start to think that if he was on the other side, he wouldn't have to deal with all the expectations. So he begins using his powers for his own gain, like scaring people to get money or to make others do what he wants.