[Backroads] has put together this nicely detailed writeup explaining how to make a low cost popup prop. He’s using a single pneumatic valve and a home made PVC piston to raise and lower a scary mask. He’s using an off-the-shelf 110v AC valve controller to control the valve. A flickering light, a “screamer” and a fog machine help fill out the project. The result is quite nice. We would be tempted to put a pressure sensor in front of it to optimize the scare timing.