One idea could be that Danny Phantom somehow gets transported to the Star Wars universe. Maybe he uses his ghost powers to help the Jedi or the Rebels. For example, his intangibility could be useful in sneaking past enemy defenses.
Another idea is a crossover where the Force in Star Wars has an effect on Danny's ghost powers. It could make his powers stronger or change their nature. He might have to learn to control these new aspects while also dealing with the threats in the Star Wars galaxy.
One idea could be to have Danny Phantom's powers in the Star Wars universe. For example, he could use his intangibility to sneak past stormtroopers or his ghostly energy blasts as a new type of weapon. Maybe he gets caught in a wormhole and ends up in a galaxy far, far away and has to find his way back home while getting involved in the Galactic Civil War.
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.
A more complex plot could be that there is a prophecy about a union between a half - ghost and a magical being like Star. Danny and Star initially don't believe it, but as they keep crossing paths and helping each other out, they start to see that there might be something more to it. However, there are forces that oppose this union, thinking it will disrupt the balance between the human world, the magical world, and the Ghost Zone. So they have to fight against these forces while also coming to terms with their own feelings.
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.
There could be a fanfiction where Danny is turned into a star - like being. His powers are amplified and he has to learn how to control this new form. This story could involve his friends trying to help him while also dealing with the chaos that his transformation causes in the town. For example, his new energy emissions might be causing electrical outages or strange phenomena.
The OC could be a detective - like character who is investigating strange disappearances in Amity Park. Danny and Star get involved because they suspect ghosts are behind it. The OC doesn't believe in ghosts at first, but as they start to work together, they realize that there are things beyond their understanding. Danny has to be careful not to reveal his identity as Phantom too soon. As they dig deeper, they find out that there is a powerful ghost who is kidnapping people to use their energy for a dark ritual. The three of them must find a way to stop this ghost and rescue the captives.
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.
You could write a fanfiction where Danny Phantom discovers an ancient ghostly artifact that is actually a highly advanced piece of technology from an extinct ghost civilization. He has to figure out how to use it, and in the process, he learns a lot about the history of the ghost zone and how his powers might be related to this long - lost technology. This could lead to some really cool adventures as he tries to keep the artifact out of the wrong hands.