Knowing this is basically a tragedy written on it, I do have a question.
How are ghosts different then they were in life? are they exagerated versions, more ruled by desires? are they subdued, more whisps of what they were? Does it take centuries for souls to drift from recongition?
I have a player who's character wants to go to the underworld and retrieve his wife's soul.
We haven't comprehensively worked out the way ghosts work, yet. I definitely don't think all ghosts run on exactly the same rules.