While checking out the new selections at Grandin Road I saw an awesome mirror with a skeleton coming out of it. The $500 price tag scared me off, but it did inspire me a little. Not being mechanically inclined to build something as elegant as the Grandin Road one, I did make a "poor mans" version using a loop of black thread under the arms of one of those $15 Walmart ground breakers. I then "hung" the loop around the top of a couple mirrors hanging around the house, adjusting it to get the proper angle (I tied the thread with a granny knot so I could make adjustments, then I tied a square knot when finished).
They are not nearly as elegant as the Grandin Road version which can be found at http://www.grandinroad.com/sorceress-skull-framed-mirror/halloween-haven/indoor-decor/808344 but I do like the look and the price. The skeletons are light enough so they don't seem to hurt the mirror and if a kid swats one and breaks it you I am not out $500 (we host a kids party each year). If you get close enough you can see the thread but hopefully no one will go that close.
Some ancient peoples thought they could "See" spirits" in reflections of water and later mirrors.
If you had a flat screen Tv with a video camera behind someone, you could make a "mirror" (The flat-screen) they could face and only see their own back!
Of course this could be made even better if you secretly stuck a sign on their back saying something like "Next Victim" ,0r "Watch me closely, I might be a Werewolf."Or just the age-old standby:"KICK ME!"