Mirror! If you have a "make a funny face" type sign or something similar, you could use plexi and some of the mirror film to make a non-breakable mirror.
One of the Ripley's Museums used to have one of those, and it was a two way mirror, so the one side it had a thing about how to roll your tongue and hey, here's a mirror to see if you could mimic the photos... only to discover on the way out that it was a two way mirror on the end and those around the other side of it could see all the folks making extremely silly faces. They did away with it I believe due to the increase of digital photo/phone capabilities (so those that hadn't given permission to be photographed wouldn't be captured and uploaded without their permission).
So not quite the same as the Ripley idea, but using a mirror for a drop panel might be fun if you make it look good. Get an old ornate frame, maybe have a sign about it being a "magic mirror" that shows their true love's form or something to get someone to stand there for a few seconds peering into it... could be a super scare!