The inimitable Dave Lowe has put up a wonderful tutorial on using plasticine and patching compound to quickly and easily cast small items.
This would be a fantastic way to inexpensively create decorative items. Make a mold of something like a skull or a bat, turn out loads of copies, and use them to accent things like mirrors or candlesticks. (You could also experiment with running a bunch of them along the wall as a decorative frieze.) The technique would also be handy for duplicating orphaned items, so if you’ve got a single gargoyle that you found at a flea market now you can give it a twin.