Well, one possible plot could be that Sam gets exposed to some ectoplasmic experiment gone wrong. Maybe she was trying to help Danny with something related to the Ghost Zone and ended up getting infused with ectoplasm. As a half - ghost, she'd have to learn to control her new powers, just like Danny did. She might struggle with the idea of being part - ghost at first, especially if it affects her relationships with her friends and family who might be a bit freaked out.
It could be Vlad Masters. Since he's always been interested in Danny's half - ghost state, he might see Sam becoming a half - ghost as an opportunity to gain more power or to use her against Danny. He could try to manipulate her new powers for his own evil plans.
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.
It could be that Jazz is turned into a ghost as part of a ghost's plan to get back at Danny. Once she becomes a ghost, she has to quickly learn the ropes of the Ghost Zone. She may make new ghost friends who help her understand her new existence. And she might start to develop her own unique fighting style as a ghost, different from Danny's, which could be really interesting to explore in the fanfiction.
Well, it could be about Danny having to face various challenges from other powerful ghosts who don't want him to be the king. Maybe he has to prove his worth through battles and outsmarting his enemies.
Well, perhaps in the future, Danny and Sam get married. They have a family and are trying to live a normal life, but their past as ghost hunters keeps coming back. Their kids start to show signs of having special powers or an interest in the supernatural. Sam and Danny then have to teach them about the world of ghosts while also protecting their family from old enemies that resurface.
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.
Well, perhaps Danny Phantom, in this fanfiction, could be turned into a mother due to some magical mishap. Maybe he has to deal with the daily tasks of motherhood like taking care of 'phantom kids' who have unique powers. He might struggle to balance his own heroic duties with the newfound maternal responsibilities.
In the fanfiction of 'Danny Phantom becomes a god', perhaps he first discovers his new divinity through some sort of ancient prophecy or a powerful artifact. Once he becomes a god, he could decide to create a new realm where ghosts and humans can co - exist peacefully. He might also use his powers to give certain humans the ability to see and interact with ghosts in a positive way, in order to bridge the gap between the two worlds. There would likely be a struggle as he tries to convince other powerful entities in the Ghost Zone that his way is the best for everyone.
In a 'Danny Phantom becomes villain' fanfiction, it could be that Danny has a major falling out with his friends and family. He feels betrayed and abandoned. This emotional turmoil causes him to snap and turn to the dark side. He then uses his ghost powers to take revenge on those who he thinks have wronged him, becoming a feared villain in the process.
One possible plot could be that all the ghosts in the Danny Phantom world decide to be on their best behavior for the wedding. They might offer unique gifts, like a ghostly flower arrangement that never wilts. Danny and Sam would have to deal with the normal wedding jitters, but also the added stress of keeping the peace between the living and the dead guests.