I can't get Buckaneerbabe's Eternal tombstone out of my mind.
The one I'm starting to build will have the female figure pop-up (probably more of a slow rise) to reveal a skeleton face with glowing red eyes. I just received the PVC Spider Joints from http://www.spiderhillpropworks.com/
today (awesome product by the way) and am going to use those as the inner workings of the arms. If anyone knows of a smoother movement please share. I will probably skin the arms with carved pool noodles which will then be skinned with liquid latex colored to look like stone. I played around with covering a pool noodle with latex last night and was pleased with the results. I need flexible arms so mannequin arms won't work.
These are rough build pics. I need to adjust the length of the pvc parts of the upper arm. The hands (latex ones coming from ebay, but may try mannequin hands too) will slip onto the pvc which will be secured to the top of the tombstone (wood tombstone top). The piece of pvc that acts as the spine will be on a pivot, so when the pneumatic cylinder retracks it will pull the "spine" down toward the back of the tombstone which will lift the upper body and head, which in turn will make it look like she is pushing herself up from the tombstone. All good in theory, let's see if I can build it. I'll probably attach one end of a wire to the skull and the other end somewhere else to help tilt the head up and maybe another wire to help open the jaw. Will be using a Monster Guts Nerve Center for the control and unsure what I'll use as a trigger at this time. The skull in the pic is just for perspective and will be more face down when completed.
I modified one of the Spider Joints to allow for more rotation: