Here is what I eventually decided on what the kids would see. First, they would see a wooden box with a chain around it. There would be a red strobing light in the box and if you looked closely, you would see a skeleton in there through the slats. There would be a candlestick ontop of the box, but nothing else in the room (originally, the room had more elements, but I ran out of time and sometimes simpler is better). Then, they would see a ghostly skull with flowing white hair float up out of the box and disappear through the ceiling. and few seconds later, a full-bodied ghost would suddenly appear behind the box. As he walked right through the box, he would push aside the candlestick. He would crouch down and disappear into the box, come back out then walk through the front of it. As he steped through the front, the chain would lurch forward and rattle back against the box. He would then turn and walk through the wall. Then a giant skeleton would rip the roof off the rotating bench and reach in at the kids. That part was supposed to be scarry but I didn't get any screams from the skeleton. The kids did love the ghost, though.
So, the first thing I needed was a box. Actually, I just needed four of the six sides. So, I bought some wood and nailed the thing together. I also bought a short piece of chain from Home Depot and hooked it across the front. The chain is held in place (as you can see) by some wood screws.
I put plenty of space between the slats so that the skeleton was visible inside. The skeleton is a mixture of 4th-quality Bucky bones and some hollow plastic bones. The rib cage is a plastic breast plate from a costume. I just cut out the black plastic part. I also used some string to round out the ribcage. You can see that I used a block of wood attached to the inside of the box to support the skull. Wood screws and string were sufficient for the arms and other bones.
In this shot you can see a servo sticking out behind the skeleton. That servo has a push rod that is attached to the chain running outside of the box. When the ghost walks through the front of the box, this servo simulates the ghost kicking the chain. I will describe how I did this, but unfortuneately, the servo I used (a Hitech HS-645MG) was not strong/fast enough to make a realistic kick so I ditched this at the last minute. I think a HS-755MG would have worked but I had only one of those and needed it for the candlestick. Here is a closer look at the servo setup. One link of the chain is simply wired to the end of the push rod just outside of that hole in the board.