The skulls I bought were on a string, they were basically hot-glue-gunned at the top (there was a hole at the top of each skull), and you could see around the hole, the extra plastic that came out of the mold, which I had to cut off with an x-acto knife. I wanted the skulls to be more white, less yellow, so I sprayed all of them with primer, then touching them up with an airbrush in a dark grey color--then finished with a clear gloss.
I knew I wanted the belt to close with a clasp of some sort, so I chose to use a round clasp similar to one you would use for a necklace. I punched using an awl on the sides of each skull and strung a piece of craft wire through.
For the tiny skull on Mystique's hair, I simply hot-glue-gunned it as close to the lace-front as possible. Tacky glue will NOT work. I wore this in a club for a couple hours and this skull stayed put!
I did curl the wig a bit because it was a little too flat when I bought it.