12-14-2011, 04:44 PM
As per the Supernatural guide, only AniWayans can have "spirit guides" per se. That doesn't mean that other characters can't have poltergeists or worse ghosts/spirits hanging around them -- most of the ghosts we've had played or as companions before have been neutral/harmless to actively helpful -- I don't believe there have been many (if any) instances of an evil or malevolent spirit. 
It would be interesting to see, but you'll also have to take care not to let the ghost act too powerfully, too.
It would be interesting to see, but you'll also have to take care not to let the ghost act too powerfully, too.