So for whatever reason I was thinking about why Danny seemed so different than other ghosts, including Vlad. No ghosts have human skin tones and usually range around blue, green, or white, except Danny who is actually tanner as a ghost. Most ghosts have either dark green eyes or red, but Danny has bright green eyes, the same color as his ectoplasm. ALL ghosts have an obsession, including Vlad. However, Danny has none! Some people assume his obsession is saving people, but we've seen in episode like "Livin' Large" that Danny doesn't feel a need to, he does because he can. We also see in episodes featuring the Guys In White and Freakshow that Danny has no problems fighting and hurting humans and in episodes like "Splitting Images" its even more evident when Danny actually causes distress for humans, not because they're hunting him, but just for the Lols. All of these issues would point to Danny not actually having an obsession.
Note: Tucker matched all the criteria when Deseree turned him into a halfa.
There's also the issue that Vlad spent A LONG TIME in the hospital after his accident, but a month after Danny's, it's like the accident never happened. Now some people say that this, along with Danny's other differences from ghosts are because he took a full blast from the portal instead of just a head-shot like Vlad. Although I would agree that this theory would explain why Danny wasn't hospital bound, I would say this theory would hold the exact opposite on everything else. If Danny had more ectoplasm thrown at him and on a wider surface area, shouldn't he be MORE ghost-like than Vlad?
So the question is: Why is Danny so much more human like than Vlad?
My answer: Because he's not really half-ghost!!
What if Danny was a mutant or metahuman (don't mind me, just going to drop in some random DC and Marvel terms) that could absorb energy? When he had his accident, he absorbed the ectoplasmic energy in the portal and that gave him his "ghost powers" because those are basic elements to ectoplasm. There are actually little hints in the show that could make this true!!!
Note that Danny suddenly seems to get better at using his powers as he faces his first major ghost, Lunch Lady. As he faces more ghosts, Danny would absorb more ghostly energy. Danny gains overshadowing after coming into contact with an amulet that likes to essentially possess people. Danny becomes better and better at duplicating the more times he faces Vlad. Danny only discovers his ability to overshadow technology after facing Technus. Danny "miraculously" gains his ghostly wail after being beaten by his "Older self" (I'll get to Dan in a second). Danny gains ice powers only after passing through Frostbite's realm. And lets not forget that the ENTIRE PLOT of "Torrent of Terror" was that Danny absorbed Vortex's weather controlling powers. Another thought to think about was Danny's immunity to Ember's music at first. Could it be that he was absorbing the small amounts of ghostly energy within her songs and that's why he was immune, only really being affected when he faced her in RL and when she was stronger? Also, why could the other ghosts remember what had happened while under Freakshows control so easily when they were under longer than Danny and he was mostly blurry? Perhaps because he wasn't the one being controlled, but the energy inside him and he was in more of a mental stasis.
This could also explain why Vlad had so many problems producing a halfa with Danny's DNA. He was trying to force the DNA into being something it just isn't. The only semi-stable clone was Danielle, and that was obviously the work of genetic manipulation considering she somehow developed an X chromosome where a Y one was supposed to be.
So what about all the times Danny's lost his powers or been separated from his "ghost half"? Well, I can explain that too! Let's start with the first cause of a separation, the ghost catcher. The device was meant to "separate ectoplasmic energy from people" and that was exactly what it did. It took all of the ghost energy Danny had compiled and sucked it out of him, but of course that much energy wouldn't just disperse. It combined together to create a new ghost and (like all ghosts) used the human it had once been as an imprint. Since it is just a ghost though, we can now see that "super hero" obsession everyone always believed Danny had, what with the bed sheet, retro-batman-like phrases, and deep voice. The separation didn't leave Danny unharmed though. it created a slight neurological imbalance from the ghost taking part of his psyche. When he passed through the "separate" side once more his powers and the ghost's not completely developed duplicating powers acted up, splicing the two together while the two psyche's pulled apart, leaving the two with half of Danny's life force and half of the ectoplasm (obvious by the separation of powers between the two) each, creating what would have been a pair of halfas, were it not for the far too small about of life energy, something that very well could have been a problem had they not fused back together so quickly, returning Danny back to himself.
Next are Vlad's two devices, the cube he uses in "Bitter Reunions" and and the Plasmius Maximus. The cube is obvious. In the words of the Danny Phantom wiki, "The Spectral Energy Neutralizer... takes away Danny's ghost power from inside." It literally sucks the energy away, making it unusable until he is released and able to reabsorb it. Unlike the others so far, the Plasmius Maximus doesn't suck away the ectoplasm, instead it neutralizes it, effectively shorting out Danny's powers for three hours, something which would just as easily work on a true ghost, as we see its used on Vlad later that episode.
And then we get to Dan. The fun thing is we never get any big info on Vlad's wolverine claw things, so we can take full liberty with this one. They could work similar to the ghost catcher, meaning they removed all the ghostly energy from Danny, but since Vlad had meant for Danny not to have any "pesky emotions" they didn't have the little neurological bug the catcher had. Meaning Dan was essentially a blank slate when he was created. Of course, he would be aware of the man stabbing claws into his stomach and would lash out. Then, when he combined with Vlad's ghost half, portions of his obsession came through. Since Maddie and Jack were no longer alive, he wouldn't hold those parts, but he would still feel the hate, anger, jealousy. And with those three emotions as his guide, he went about destroying the world.
I'm not going to blather about the Fenton Crammer. It works the same as the Plasmious Maximus, but slower, no time limit, and that whole shrinking thing. Then the "Eco-stop-o-power-ifier" is the same as that, minus the shirking and it has a limit so that Danny's form isn't neutralized, but the energy that's used to change him back is.
So that's the random theory/head-cannon I came up with at 2 in the morning. Any questions?