My idea for Danny is that being a halfa isn't being an entirely new species of undead, it's that he's like a frozen in time model of the moment a human can become a ghost.
Danny is both the human soul that left the imprint AND the imprint itself that has latched onto said soul. Very close to haunting his own corpse, but also haunting his soul with it, like a complicated and permanent overshadowing.
And this creates a feedback loop.
His imprint half, or ghost, feeds on emotions to create ectoplasm but cant fully absorb environmental ectoplasm due to being connected to a human soul. Ectoplasm feeds and heightens the emotions felt by the soul half, or human, which then feeds the ectoplasm at a hightened level due to how connected those emotions are to it, which feeds the ectoplasm, which feeds the emotions, AD nauseum. This is why balance is so important.
If he were more ghost than human like Dani, his ectoplasm wouldn't have a stable source fuel from the lack of emotions, due to not being able to absorb ectoplasm from anything else and destabilize.
And if he were more human than ghost like vlad, he'd have too many heightened emotions and not enough ectoplasm to burn it off. Sure what he would have would be supercharged, but he'd be impulsive and dangerously obsessive, much like how vlad is.
Being the perfect balance is key.