Decided to build a new pneumatic prop this year. I had a pvc mechanism for a pop up I re-purposed inside a half coffin. I plan on setting the coffin at a 30ish degree angle and making it look like it is half buried/sticking out of the ground. Built the coffin out of fence pickets, couple hinges and 2 screen door openers converted to actuators.
I also put together a controller with an arduino and some other parts I had. It plays an ambient loop, then a triggered scare sound while operating the relays for the pneumatics.
Just need to find a mask, plumb the exhaust and finish wiring it all up.