An Example from The Haunted Theater
It's Alive!
This is a great effect if you have a lot of self control. The basic idea is to use body language to convince your victims that you are simply a dummy with a mask and loose costume. At the right moment, you move just ever so slightly.
We used this technique with great effect on the people waiting in line in the lobby. The victims have time to get used to your presence and usually discuss whether you are real or not. If you are really good at this, you can convince them quickly.
One way to look "fake" is to lean stiffly against a wall, as if someone propped a dummy there. This artificial pose usually is enough to convince most of your victims that you are inanimate. Your costume should include some sort of face covering such as a veil or some makeup to make you look less real.
As you watch them discuss you, decide on your victim. Pick the one who shows the most doubt in their eyes. Then, when the others are not looking and only your victim is watching you, turn your head just a tiny bit to look at them. Make sure that only your victim sees you do it.
This usually causes your victim to do a little jump and perhaps a squeak, and you then watch as he or she tries to convince their companions that they saw you move. If you can repeat this several times before they enter, you will have at least one of the party totally primed and ready to jump at shadows... which will in turn spook the others.
Another trick is to wait until they have convinced themselves that you are fake. Wait for them to turn away for a moment. You quietly step closer towards the group and resume absolute stillness. As your victims turn back towards you, it will seem as if you materialized next to them and they may jump out of their collective skins.
Another way to take advantage of this technique is to have a coconspirator across the room cause a distraction for a moment. When all eyes are off you, you slip out a nearby exit. Then peek and watch the consternation as the whole party who convinced themselves you were fake start to have serious doubts. They will spend the rest of the trip through the haunted house expecting you to reappear just as suddenly. This is great priming for the victims before they actually enter the Haunted House.