Well, you could have a time - travel plot in the 'Danny Phantom: The Dark Prince' fanfiction. Danny travels back in time and accidentally changes something that leads to the creation of a more powerful and evil Dark Prince. Now he has to figure out how to fix the timeline while also dealing with this enhanced threat. Or perhaps a plot where the Dark Prince gains the ability to possess humans, and Danny has to find a way to stop him without harming the innocent people.
A third plot idea is that there is a prophecy about the 'Prince of Darkness' in the Danny Phantom universe, and Danny is unknowingly fulfilling it. As he continues on his adventures, he starts to notice strange coincidences that seem to be leading him towards a dark destiny. He then has to decide whether to fight against the prophecy or try to understand it and use it for good.
One plot idea could be a team - up. Maybe Fem Pariah Dark has a change of heart and decides to help Danny Phantom fight a greater evil that threatens both their worlds. It would be full of action and interesting character dynamics as they learn to work together.
One idea could be that Danny has to face Pariah Dark again, but this time Pariah Dark has some new and unexpected powers. Maybe he has found a way to control the Ghost Zone in a different way that poses a huge threat to Danny and the human world. Another plot could be Danny trying to understand Pariah Dark's past to find a weakness. He could discover some ancient secrets about Pariah Dark's origin that no one else knew.
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 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.
Well, here's a plot. In a strange turn of events, Danny's ghost powers start to interact with alicorn magic in unexpected ways. This causes chaos in both worlds. The alicorn and Danny must work together to figure out how to stop the strange energy fluctuations. They might have to travel to different dimensions within their universes to find a solution. Along the way, they meet other characters from both franchises who either help or hinder their progress.
One idea could be that Danny is experimented on by a new group of ghost hunters who want to find a way to permanently strip him of his powers. They use some high - tech equipment that has unforeseen effects on his ghostly half, causing him to have strange new abilities. Another could be an experiment gone wrong in the Ghost Zone that Danny has to deal with the consequences of, like accidentally creating a new type of ghost. Maybe Danny himself decides to conduct an experiment to see if he can control his transformation better, but it backfires and he gets stuck in his ghost form for a while.
One idea could be that the twin has a different set of powers. For example, while Danny can go intangible and invisible, the twin might have the power to control time on a small scale. This would create interesting scenarios where they have to work together, like when Danny is in a tough fight and the twin uses time - control to give him an edge.
Well, perhaps in the fanfiction, Undergrowth could create a parallel dimension filled with his overgrown plants and trap Danny there. Danny then has to navigate this strange new world, make allies among the plant - like creatures that are also being oppressed by Undergrowth, and find a way to break out and stop Undergrowth from spreading to the real world. This would be an exciting adventure full of mystery and discovery for Danny.