Perhaps in this '10 Years Later' fanfiction, Danny has become a sort of legend in the world. He has to deal with younger generations of ghosts and humans who either idolize him or are skeptical of his methods. There could be a new villain who is aware of Danny's past and tries to use it against him. Danny may also be exploring new aspects of his powers that he didn't know about before, like the ability to travel to different dimensions related to the ghost zone.
Obviously Danny Phantom himself would still be a main character. His friends like Sam and Tucker would likely also be important. They've probably grown and developed new skills over the 10 years.
A Danny Phantom and Ben 10 crossover fanfiction would be full of action and adventure. The two characters have very different power sets. Danny has his unique ghost powers such as flight, invisibility, and ecto - blasts. Ben, on the other hand, can transform into a variety of aliens with different abilities like Four Arms' great strength or XLR8's super speed. In the fanfiction, they could be brought together by a common enemy that is threatening both the human world and the ghost zone. They would have to learn to work together, with Danny using his knowledge of the supernatural world and Ben using his combat experience from different alien forms. Their combined efforts would make for a thrilling story as they face challenges that neither could overcome alone.
It could be an evil scientist who has found a way to combine ghost and alien technology. He wants to use this to take over both the human world and the ghost zone.
One possible plot could be that Danny and Ben meet when a powerful interdimensional villain is causing chaos in both their universes. They initially misunderstand each other and get into a small fight. But then they realize they need to work together. Danny could use his ghost powers to phase through objects and surprise the enemy, while Ben could use his various alien forms to combat the villain's different attacks. For example, using Heatblast to counter a cold - based attack from the villain.
One interesting crossover could be the characters teaming up to fight a common enemy. For example, Danny Phantom's ghost - fighting abilities, Ben 10's alien forms and Kim Possible's martial arts and problem - solving skills could be combined. They might face a powerful villain that neither could defeat alone.
It's really hard to say. Danny has some incredibly powerful ghost abilities like intangibility, flight, and his ghostly wail. But Ben has access to so many different alien forms, each with their own unique powers. However, if we consider the fact that Danny has a connection to the Ghost Zone which gives him an almost unlimited source of power in a way, he might be the most powerful. But then again, Ben in his Alien X form has near - omnipotent power. So it really depends on how you define 'powerful' in the context of this crossover.
In this fanfiction, it could be that Danny Phantom meets a Danny Phantom from a parallel fan - made story. At first, they don't trust each other. But as they learn more about each other's worlds, they realize that there are some common elements that are being threatened. It could be that a powerful ghost is trying to rewrite all the fanfic universes related to Danny Phantom. So, they must combine their strengths and knowledge to stop this from happening.
Well, in this kind of fanfiction, Danny could be controlled by an ectoplasmic parasite. The parasite latches onto Danny and takes over his actions. His eyes might glow a different color to show he's not in control. His friends would first be confused, then realize something is amiss and start investigating.
There could be a fanfic where Danny and Ember accidentally swap powers. This leads to a series of comical and also dangerous situations. Danny has to figure out how to control Ember's power of influencing people through music while Ember struggles with Danny's more combat - oriented powers. It could be a story full of self - discovery for both of them.