Other then "Houdini's Great Escape", the park does not have a dark ride or a haunted house. I think the park could really use one of these attractions rather then another coaster. Something like "The Haunted Mansion" at Disney. Set in a Gothic castle or mansion with things the pop out at you and creepy scenery. Behind the Dark Knight where Chiller's station is would be great!

As for a theme, it could be just an old house that is haunted. Or, the park could base the ride on the Ghoulmaster and his ghosts. That would be very interesting! I would want it to be a ride through though. Almost like you are exploring the Ghoulmaster's castle and you will go past diffrent illusions and into diffrent rooms.