One interesting plotline could be Danny's secret identity being revealed at school in a very unexpected way, like during a science experiment gone wrong. Maybe the ectoplasm reacts with something and his powers are exposed in front of the whole class.
A possible plotline could also be that the school is built on an ancient ghostly portal. Danny discovers this and has to deal with the consequences. He might have to protect his schoolmates from the ghosts that start emerging from the newly - activated portal while also trying to keep his identity as Danny Phantom a secret from the school staff and most of his classmates.
Well, obviously Danny Phantom himself. He is the central character as the story likely revolves around his experiences at school and the revelations that occur there. Then there's Sam and Tucker, his best friends. They are always there to support Danny, whether it's helping him keep his secret or getting involved in the ghost - related adventures that often spill over into the school environment.
Another plotline could involve jealousy among the members of the harem. Each character might have their own reasons for being attracted to Danny, and when they see him spending time with others in the harem, it could lead to some intense emotional moments. This can create a lot of drama and character development.
One possible interesting plotline could be Danny facing a new and more powerful ghost that has a personal vendetta against him. This would test his limits and force him to discover new powers or ways to fight.
One possible plotline could be Evil Danny trying to corrupt Sam. He might use his powers to manipulate situations and turn Sam against their friends. For example, he could make it seem like their friends are in danger when they're not, just to make Sam question their loyalty.
One interesting plotline could be Danny facing a new and more powerful ghost that he has to defeat to protect his town. Maybe this ghost has abilities that are completely different from what he has faced before, forcing him to develop new strategies.
One interesting plotline could be Danny learning unique ghost powers from Clockwork. Since Clockwork has control over time, Danny might gain the ability to manipulate time in some ways, like seeing into the past or future of a ghost's existence. This would add a whole new dimension to his battles and adventures.
Well, a great plotline often seen in Danny Phantom College Years fanfiction is Danny's love life in college. He could meet a girl or guy who is initially unaware of his double life. As their relationship progresses, Danny has to figure out how to handle his feelings while also keeping his secret. There could be some really sweet and tense moments as he tries to protect his loved one from the dangers of the ghost world while also maintaining a normal college relationship.
One possible plotline could be Danny's internal struggle as he starts to transform into Dan. Maybe he battles with the emerging dark thoughts and tries to resist the full transformation. Another could be how his friends and family react to the changes in him. They might initially not recognize the signs and then be horrified as he gets closer to becoming Dan.
One plotline could be Danny having to deal with an ancient ghostly prophecy as the Ghost King. For example, he might be the key to preventing a great disaster in the Ghost Zone or the human world.
Well, in some 'Danny Phantom Betrayed' crossovers, Danny might be betrayed by a love interest. For example, if it's a crossover with another show and he falls for a character from that show, but that character betrays him for their own gain or because of some hidden agenda. It could lead to Danny having to reevaluate his trust in people and also face new challenges that come with the heartbreak and the betrayal. Also, he could be betrayed by an authority figure in a crossover universe, like a powerful wizard or a superhero leader who turns out to have ulterior motives.