How would Danny's ability to turn other people and things intangible fit in with your ghost physics? (It's been ages since I watched the show so I don't remember if other ghosts are shown doing that too.) Also, what about ghosts possessing people?
OOOH SHOOT THAT FIRST ONE MIGHT BE A HOLE IN MY THEORY!
With a lot of energy ectoplasm can force regular matter to behave like itself (which is how Danny does that meat and denim vapor tail), but I described phasing as atomized 4D motion... and if you atomize regular humans they, uh, die? Within this current model I think the only way Danny could safely pull living objects outside of 3D space is through teleportation, aka the more nauseating form of phasing. I guess I could also explain it as phasing all the matter around the person instead of their body, which defies canon but is most plausible; or bullshit up a way for it to be non-fatal, like their nervous system molecules staying close enough together to maintain their brain function. Even if it doesn’t kill you, the latter option sounds like an extremely unpleasant experience...
Honestly, if I were to make Ghost Physics a straight-up AU as opposed to an... elaborate network of headcanons? Phasing non-ghost organisms is one of the things I would trim off of established canon. To me it makes more sense, and creates some interesting scenarios... Trying to phase any regular matter would rattle around its atoms and have some of them swap places, subtly fucking up any phased object. Trying to do it to an organism would result in a nasty burn or death, doing it to stuff like clothes might have slight effects on texture and structural integrity, doing it to stuff like phones and PDAs would wipe their memory (or worse, make them non-functional). The same thing would apply to Danny’s clothes and any object he has in his pockets when he transforms, since he’s literally destroying and remaking them. I hope he’s good at memorizing phone numbers!
For possession, I’m pretty sure I can explain it as a ghost “storing” their normal body in 4D space; then their ecto-signature overlaying, overpowering, and remote controlling a human nervous system instead. It’s... probably actually really dangerous for the host... since the ghost is tugging around on their actual neurons... I can easily see long term possession or “messy” takeovers resulting in death or brain damage :(
To most sensors, Danny’s setup seems identical to possession or even a regular ghost, since he has that characteristic 4D hole to the GZ “behind” him. But Danny isn’t stashing a secret ghost body in 4D space (instead he converts himself into one) and his ecto-signature isn’t repressing his human nervous system, he just thinks with both simultaneously.