Perhaps Danny has an encounter with a powerful and malevolent ghost that corrupts his mind. This evil influence makes him see the world in a different way. He starts to view humans as weak and unworthy of protection. As a result, he uses his ghost powers to cause chaos, attacking both humans and other friendly ghosts. He could even form an alliance with some of the more evil ghosts in the Ghost Zone.
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.
In a fanfiction, Danny could become evil if something happened to his family or friends. For example, if they were threatened by the government because of his powers and he felt betrayed. This could lead him to believe that the world is against him. He then decides to use his powers to fight back in a very extreme way. He turns to dark magic or forbidden ghost powers that slowly corrupt his soul, making him into a villain who wants revenge on the whole world that he thinks has wronged him.
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.
The Guys in White could be the main antagonists. If Danny becomes evil, they might see this as their chance to finally capture and experiment on him. They would be constantly chasing him, which would make Danny see them as the main obstacle in his new evil plans, and thus they would be the antagonists in the story.
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.
One possible plot could be that Danny Phantom, through some magical mishap or powerful spell, is transported to the world where Jack Frost exists. Danny has to figure out how to get back home while also dealing with the new powers and rules of Jack Frost's world. He might start out as an outsider but gradually gain the respect of the other winter spirits as he uses his ghost - fighting skills in a new way.
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, 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.
In this fanfiction, it could start with Danny Phantom turning evil due to an experiment gone wrong. As for Sam, she has always had a special relationship with plants. The evil Danny might start to use plants as his minions, controlling them to do his bidding. Sam, seeing this, decides to take matters into her own hands. She begins to study ancient plant lore to find a way to break Danny's control over the plants. Along the way, she might face many challenges, like Danny sending his plant - minions to attack her. But she doesn't give up, as she is determined to save Danny from his evil state and restore the balance between the supernatural and the natural world.
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.