Well, in some 'Danny Phantom Adopted by Ghosts Fanfiction', a possible plot is Danny forming unexpected alliances with other ghostly beings as a result of his adoption. He could team up with some outcast ghosts to fight against the more malevolent ones. Also, his adoption might lead to a series of adventures where he explores different ghost realms that were previously unknown to him. It could be really exciting as he discovers new landscapes, creatures, and mysteries in these realms. And perhaps, there is a plot where Danny has to prove himself worthy of his new ghost family in the face of some ancient ghostly trials.
Obviously, Danny Phantom is a main character. Then, there are usually the ghosts who adopt him. These could be powerful and unique ghosts, like some ancient spectral beings with their own personalities and motives. There might also be his human friends who play a role, even if they don't know about his adoption. They could unknowingly influence Danny's actions in the human world which in turn affects his situation in the ghost world.
In the fanfiction 'Unexpected Adoption', Danny is adopted by a powerful ghost who has his own motives. This changes Danny's view of the ghost world completely. He has to learn to navigate this new relationship while still dealing with his human life. It's a really cool take on the idea of Danny being adopted, as it shows a different side of the Danny Phantom universe.
One possible plot could be that Danny is kidnapped by a new ghost enemy who wants to use his powers for their own evil deeds. Maybe this enemy plans to drain Danny's ghostly energy to become more powerful. Another plot could involve Danny being kidnapped by a group of his human enemies who have finally discovered his secret identity and want to experiment on him. Or perhaps a time - traveling villain kidnaps Danny to prevent him from ever becoming a hero in the future.
One possible plot could be that Danny's sneeze accidentally activates a new ghost power. For example, every time he sneezes, he temporarily gains the ability to phase through different dimensions. This could lead to all sorts of adventures as he tries to control this new and unexpected power while also dealing with his regular ghost - fighting duties.
Maybe Danny and a ghost enemy are stuck together due to some strange ghostly spell. This forces them to understand each other better as they try to break the spell. As they are stuck, they start to see the other's point of view, which could lead to an unexpected friendship or at least a truce.
One possible plot could be that the evil Danny Phantom tries to manipulate Sam into helping him take over the Ghost Zone. He might use his powers to deceive her at first, but Sam gradually realizes his true intentions and has to find a way to stop him.
Well, one interesting plot could be Danny finally revealing his secret to his best friend Tucker in a really dramatic way. Maybe it's during a ghost attack and he has no other choice but to show his powers to save Tucker. Another plot might involve Danny's parents finding out his secret through some accidental discovery in their own ghost - hunting experiments.
In a more emotional plot, Danny has lost his family in some ghost - related incident and is all alone. Batman, seeing a kindred spirit in Danny (both having experienced loss), decides to adopt him. Danny then has to adjust to living in the Batcave and being part of Batman's crime - fighting family. He struggles with fitting in at first but eventually finds his place and becomes an important asset to the team, using his powers in ways Batman hadn't thought of before.
In some Danny Phantom harem fanfics, a common plot is Danny accidentally creating a harem situation. Maybe he saves a group of girls from a ghost attack and they all become infatuated with him. Then he has to balance his normal life, his ghost - fighting duties, and his new relationships with these girls. It can lead to a lot of comical and heart - warming moments as he tries to understand their feelings and his own.
One plot idea could be Danny having to deal with the politics of the Ghost Zone as the King. He might have to face different ghost factions vying for power or trying to overthrow him. Another could be Danny exploring the secrets of his new - found kingship, like hidden powers or ancient prophecies related to the King of All Ghosts.