He is created by a human, assembled from multiple bodies, something’s going to look wrong. The parts might look out of proportion to each other and some of the muscles might be twisted as if they are attached strangly. This doesn’t mean you can ignore anatomy, your monster will be far more believable if you draw real anatomy then twist it a bit. Pay more attention to the shoulders and arms since they are in the light and need to be drawn more carefully than the lower half of the body.
After your figure is constructed, really work with shadows and bring the lit areas forward. The contrast on this piece needs to be strong (we’re betting that it’s lit by lightning from above left). Be sure to lighten the shadows as they get further from the light source, this will imply an atmospheric light that is reflecting off the mountains and back onto the creature. For the shadows don’t just draw blacks, put details into the shadows. To make the stone believable, change the direction of your shading and vary the textures. Draw ripped up clothes wrapped over the arms and legs.
Really tighten the shadows up. Add little highlights in the shadows to mimic reflected light from the fires below and to the right. Refine and clean up the edges and smudges. Use an eraser to pull the highlights out of the pencils.