Disclaimer: I do not own Danny Phantom or anything else that appears or is mentioned in this story with all content belonging to its respective owners and I am in no way shape or form attempting to or making a profit from this work of fiction.
Alright a quick theory on Dan Phantom, Danny's future and evil counterpart, on why he can't be pure evil and, in my opinion, just mentally unhinged.
Reason one is simple, Danny has been stated to have unimaginable willpower and from this he was able to force Pariah Dark back into the Sarcophagus of Forever Sleep and then keep him there despite his struggles with very little power left, 1% to be precise. So taking this into account I find it very hard to believe that Vlad's own ghost half was able to overwhelm Danny's own. And taking account of the episode "Identity Crisis" it is shown that his ghost half is immensely heroic, annoying in my opinion but that's a topic for another day, after being split from his human half. So taking this as canon it leads to reason two which is I find it hard to believe that Danny's ghost half was so easily subdued and possessed by Vlad's own. Not to mention his actions of removing Vlad's ghost half makes no sense unless you take into account the process to be immensely painful and thus the ghost half of Danny, which I will now refer to as Dan, wasn't thinking very clearly when he did separate Vlad's ghost half but then his movement to overshadow Vlad's ghost half makes even less since. Wouldn't it make more sense for Dan to merge with Danny again in an attempt to fill what was most likely a hollow feeling in himself due to the separation? So I ask you, how does any of this make sense? Why did Dan do what he did the moments after the separation of him and Danny? So, with all this in mind I'll go to the real reason on how Dan even came to exist. The sheer insanity of life did it to him.
How does that make any sense you may be asking? Well I'll answer it right now with a very simply statement.
WHAT THE HELL!
How is a condiment for a burger explosive? How is Danny cheating on a test, a single test, leading up to something like that? Not to mention this was the one and only time it was ever shown in the series and for an admittedly good reason. Mr. Lancer himself stating that the test would decide his future and Danny would probably have little time to study with ghost attacks so he did what he thought was best for his future. But back to the topic at hand, an explosive condiment, the sheer ridiculousness of it making me want to stop writing this right now even when I'm even thinking about it, took away his friends and families with everything that caused it happening just because he cheated on the test? Really?! That would drive anyone to the deep end and straight off it in a heartbeat and Dan did seem a bit insane in my opinion. But hey, I can go on and one about this for a long time but in the end I'll just say this.
Dan Phantom is not evil, he's just completely lost his mind at the sheer insanity that took away his friends and family. Besides, if he was evil, he would have just destroyed the planet, which seemed highly possible for him given how Clockwork, a ghost that has never intervened at any time for any of Danny's many problems, decided to step in and stop him, at least for a moment.
So you can believe what you want but in my mind Dan Phantom isn't evil, he's really just insane or consumed by grief that he refuses to let go and grief can turn to anger, I think Yoda said that, but in his riddle talk but this is just a theory on my part and you don't have to agree with me, I'll actually be glad if you disagree and argue my opinion.
As long as it remains civil and mature that is.
Okay, onto a less serious topic for a theory I'll look into the basis of a few ghosts and their powers so to start it off we have Skulker and his is obvious with it being hunting, a thing that both his realm and he himself represent, at least when it's not concerning Danny Phantom AKA the most elusive prey ever, and he himself stated multiple times that he is the greatest hunter in the Ghost Zone.
Next is Ember, with a once again obvious source of her powers being music based on her choice of clothing, her music abilities based around the playing of her guitar, her overall attitude and comments when using a power. So yeah, music is her source of power, pretty clear actually.
After Ember I was thinking of doing the Box Ghost but decided on Clockwork and his power is simple and I think I already mentioned it with it being based on drawing power from the timestream and I'm almost a hundred percent sure that I mentioned his reason for keeping Danny alive was to keep his powers strong.
Next comes Nocturne with the obvious power source of sleep and dreams, actually showing it in the show by absorbing the energy created by the dreams of others and able to grow stronger and stronger as he absorbs them. An interesting power and it also leads me to something else.
A third theory on the energies in the show with the mundane like electricity to ghostly and the subcategories of it like dream and music to name a few. So where does it all come from, how does any of it make sense? How can you possibly get energy from dreams or times or hunting? I'll leave that question to you, post a review on it and I'll be sure to answer back.
Peace.