Have you seen the haunted window videos. They show putting a tv under the window and a 45degree peice of plexiglass to form a Pepper's Ghost Illusion. You could use a black sheet of cardboard with writing on the floor( instead of a tv) and a light with a dimmer to make the words fade in and out. A live actor can be behind it or even project the other ghost on a rear screan behind it. Look up Pepper's Ghost on You Tube.