First you create a tiny scene inside a box. Leave a peep hole in the front so you can look inside at the miniature room.
This is what the miniature scene looks like when you look in the peep window. No ghost in this picture.
If you look carefully you will see the ghost is materializing in front of the fireplace. The illusion is hard to get on film. It looks so much cooler in real life.
This is how the illusion works. The real ghost is hiding out in a corner. When the light comes on she reflects into the piece of plastic between her and the miniature room. Very cool!