One idea could be Danny making new friends at the Ghoul School. He could learn about different ghostly cultures and powers there. Another idea is a mystery at the school, like something disappearing and Danny has to solve it. And perhaps Danny could teach the ghouls about the human world in return.
Well, you could write a fanfiction where Danny Phantom has to take part in a special competition at the Ghoul School. It could be a race or a battle of powers. Maybe he teams up with some of the ghoul students who are initially reluctant to work with a half - ghost. This would lead to some great character development and interesting interactions between different species.
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.
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.
A great idea for a Danny Phantom monster fanfiction is to explore the origin of some of the monsters. Maybe Danny stumbles upon an ancient tome that reveals the true beginnings of the monsters he fights. This could lead to him having a different perspective on them. Or perhaps there's a fanfiction where a monster falls in love with a human and Danny has to navigate the complex situation, as it goes against the natural order of things in his world.
Maybe in the fanfiction, there is a device that can steal powers, and it targets both Danny and the Flash. They have to team up to stop the villain who has this device. Danny could use his ghost sense to detect the villain's presence while the Flash could quickly get them to the location. Their combined efforts would lead to a great adventure filled with action and some humorous moments as they learn to work together.
One idea could be that Danny Phantom gets sucked into the Deltarune world. He could use his ghost powers to help the characters in their quests. Maybe he teams up with Kris to fight against the dark forces in the Dark World.
Well, you could focus on the relationship between the apprentice and Danny's friends. For example, Sam and Tucker might be a bit skeptical about the new apprentice at first. The apprentice could try to prove themselves to Danny's friends while also learning the ropes of being a ghost - hunter. Or perhaps the apprentice has a special connection to a certain type of ghost, like they can communicate with them in a unique way, and this leads to an adventure where they have to use this connection to solve a mystery.
Well, perhaps the lair is located deep within an old, forgotten mine. Danny could have discovered it while exploring and made it his own. He could use the tunnels for training and storing his ghost - fighting gear. There could also be natural formations in the mine that he uses as traps for any ghosts that manage to find their way in.