One idea could be that Danny possesses someone to experience a normal day at school without his ghostly powers causing chaos. He could learn about the simple joys and struggles of being a regular human for a day.
Perhaps Danny accidentally possesses an animal. This would be really fun as he has to figure out how to control the animal's body and communicate with his friends. He might also discover new abilities or limitations that come with being in an animal's form, and his friends would have to figure out how to turn him back.
One idea could be exploring what would happen if Danny had a different body form due to a ghostly experiment gone wrong. For example, his body could be part human, part animal ghost hybrid, which would bring a whole new set of challenges and adventures as he tries to hide this new form from his friends and family while still fighting ghosts.
One idea could be that Danny gets an illness that affects his ghost powers. For example, he might start losing control over his intangibility or invisibility. This could lead to some really comical or dangerous situations. Another idea is that his friends try to find a cure for his strange ghost - related illness while also keeping it a secret from the town.
One idea could be exploring Danny's relationships in a different way. For example, how his friendship with Sam and Tucker might develop if they faced a new supernatural threat. Another could be a story where Danny discovers a new power and has to learn to control it while dealing with school and his ghost - fighting duties. And perhaps a fanfiction where Danny travels to an alternate dimension within the Danny Phantom universe.
A great fanfiction idea could be a time - travel story within the Danny Phantom Phantom Planet universe. Danny somehow gets sent back in time to before he became a half - ghost. He has to figure out how to get back to his own time while also dealing with the knowledge he has of the future. This could lead to some really interesting interactions with his past self, his family, and friends. And he might accidentally change things in the past that could have a huge impact on the future of the Phantom Planet.
Well, there's 'The Dark Possession' fanfiction. In this story, Danny is possessed by a powerful and malevolent ghost, and it shows his struggle to break free and save his friends and family. There are also some fanfictions that explore the idea of self - possession, like 'Danny's Inner Struggle', where Danny has to deal with a part of himself that seems to be taking over in a way.
Well, a possession by an ancient spirit might be cool. For example, an ancient hero's spirit takes over a RWBY team member. This could bring out new fighting styles and knowledge that the character didn't have before. They could use this newfound power to face a greater threat. Also, an alien - like entity possessing a character could introduce some really strange and unique abilities and challenges for the other characters to deal with.
One idea could be that Danny discovers a new ghostly power that he uses to take revenge on a group of bullies who have been tormenting his friends. He could use his intangibility in a creative way, like sneaking into their lockers and making their things disappear.
One idea could be Danny Fenton having to deal with a new ghostly enemy that can manipulate time, making his double life as Danny Phantom even more chaotic. Another could be Danny trying to balance his high school life, including exams and relationships, while also facing a ghost invasion that only he as Danny Phantom can stop. Or perhaps a story where Danny Phantom discovers a hidden power within himself that has a connection to his human side, Danny Fenton.
One idea could be exploring Danny's new role as a hero on a global scale. Maybe he has to deal with new threats that are attracted to his increased fame. Another could be delving into his relationships with his friends and family after the big events in Phantom Planet. For example, how does his relationship with Sam and Tucker change now that he's a more public hero?
One idea could be Danny Phantom using his powers to help during emergency situations like in 911 calls. For example, he could use his intangibility to reach victims trapped in collapsed buildings.