I worked on a possible Halloween pop-up card today.
It needs some work. I really wanted the ghost to be rising up behind a gravestone or a tomb, but I haven't been able to find a piece of vector-based that works for me.
The mechanics, based on my Birthday Cake card, work really nicely, though -- the ghost rises up nicely through its slot when you open it up.
I'm also looking for a better quote to put on the outside.