Monster from nothing
I'm sure you've all seem plenty of magic shows where the magician makes his assiastant vanish right before your eyes... Well I once built an illusion that was along the same lines and I think it can be used in a haunt to create a really cool effect. The way it is suposed to work is that you put someone in a large box and close the lid. You then Tip the box over and open it up to reveil a now empty box. Tip it back upright and open it to reveil the same person but now they're in a different outfit. Pretty cool if done with a lot of practice.
Here's the twist I was thinking of using for a haunt. Instead of starting from the begining where someone gets in the box, jump ahead to where the box is shown empty and have it upright itself and a monster jump out of it. Maybe like this... customers are making their way through the dark hallways of you haunt when they come upon an empty box with no one else around it.. as they get closer it starts to shimmy and the lid swings shut... the box starts shaking and they hear an awful sound... wham! the box top slings open and out comes your monster!
Sorry, I'm no writer, but I hope you get the idea...
Here is how the illusion is done, looks simple and it is. Its all in what the eye tells your brain. It looks like an empty box when Tipped Over and opened. The trick is that you can't tip the box while its open.