The Haunted Mirror is a wicked cool illusion. I got a great deal on a commercial grade flat screen TV, and built a wooden frame to hold a two-way mirror over the front. A Raspberry Pi runs a video-only loop of my son wearing a creepy goblin mask.
The way it works is simple. The TV is always displaying a black screen. The video is shot on a black background, so when the goblin is lit, it shows through the two way mirror. When the TV is just showing black, the two-way mirror works as a regular mirror.
I'll be uploading a video of it soon. Stay tuned.