>>56217664I think the most common is that they're just pokemon that appeared one day and they're a bit more mischievous than others. Sometimes they're associated with the death of pokemon or in rarer cases humans, but that seems to be the exception rather than the norm.
As for how they engage with their humans, I think the most common theme I see with them is that they tend to be possessive of their trainer, pun intended, and can sometimes go overboard with it which is a bit much for some people. The anime has touched on this several times, like the ghosts in the tower that murdered Ash and didn't want his ghost to leave them, or webmrelated where some fuckhead ditched his gengar to chase after women.
