I know I always say this, but the best reference for hands is your own hands. On the first pass, I drew a pair of kind of lazy monster hands that had zero personality. I went back and used my hands as reference, and I'm glad I did. Although these are crazy, Alien hands, the basic structure is the same. Basically we're just adding detail long the tendons and in between the bones. Oh, and there are claws, too ;)