This one was pretty easy once I found the right base figure (thanks to Shinobitron for the idea). I'd been wanting to do this custom ever since I got a Ripclaw figure and couldn't believe how perfect the head would be.

I stuck the Ripclaw head on the Movie Joker body but it didn't quite work, seemed out of proportion somehow, so I extended the neck by about 8-9mm and widened the shoulders by about 3-4mm each. I also applied the tiniest bits of sculpt to the bridge of his nose and his chin just to make him more comic accurate. Then I shaved down the lining on his gloves so they could pass for hands, and sculpted the cuffs and cravat.
After that it was a simple paintjob using Citadel paints. I applied a very light wash around the eyes, cheeks and fingers, lined the creases on his trousers (looks more delicate in natural light than the pics), and lightly drybrushed the cravat for a velvet effect.