Scary and really nice choice of colours. His lower rocky looking body part is rather hard to undestand or to get, maybe you could see if you can improve there a bit. His negative form could also be a little more interesting. Right now he's just a big round mass. The form of the one in the back looks more dynamic and appealing I think. Maybe it would help if you'd lighten up the arm in the back so it is easier to visually break the body into plains.