But I have a twist on Ghosts,
What if a Ghost doesn't want you to solve it's great unfinished task? Be that its murder or some other crime. What if it LIKES eternal undeath? What if it doesn't want to account for its crimes in life and is pretty happy marauding the town in death.
Perhaps its unstoppable unless you can find and kill the ghost's murderer? The ghost will hinder you because it wants to continue existing and the murderer wants to hinder you because they don't want to die.
But the townsfolk? They sure are in a panic what with the ghost causing a trail of carnage. You'll first have to investigate who the ghost was, then find out who killed them, find said person and take them down. All the while both the ghost is trying to possess your body and a living person is out to kill you.
Just a thought..