Here's a VERY simple mod, it's a McFarlane DC Devastator with a DC Direct Doomsday head and a partial repaint (bones, nails and pants, I didn't really do anything to the skin). Heads of both figures were the same size, so it was a pretty easy fit. Oh, I've also used a couple of Doomsday's protrusions to make the big chest thing.

Recipe:
body - McF DC Multiverse Devastator
head - DC Direct Doomsday