Use lowmelt glue to attach the skeleton arms to the tombstone (hotmelt glue might melt the foam slab). For the copper look, sponge on Candy-Bar Brown, Black, and Metallic Red Copper acrylic crafts paint.
For an aged copper finish, mix one part each of White, Candy-Bar Brown, and Avalon Blue. Dry-brush and/or sponge the mixture onto the tombstone, concentrating on the bottom portion but not covering the entire stone. Spray on a light coat of Forest Green paint.
For a gray stone look, pour White and Black crafts paint onto a disposable plate. Dip the sponge onto both colors and, using a dabbing motion, apply on tombstone. Add Black to the sponge to make the edges darker. Rinse the sponge, and then add some White using gentle, tapping motions. Allow to dry.
For a mosslike finish, spray randomly with Forest Green spray paint.
For a weather-streaked look, use a household trim brush to brush White in long streaks adding Black as desired while the White is still wet.