Hey man, I used kneaditite, commonly called greenstuff. The best place to get it is on ebay for 16.99 for a 36 inch roll. It is workable for an hour or two. You have to periodically dip it in water as you're working on it to keep it from getting too sticky.
Looking at your Horror Show fig, what product or compound did you use to add the bulk and sculpt the puffy texture onto the torso? I am in need of something to add onto existing torsos as well.