Complex sentence: Instead of gaining the properties of a rock, as sand is just small stones, he gained a form not unlike Marvel's Sandman--a being comprised of small grains which he can manipulate in a variety of ways.
Split into simpler sentences: Instead of gaining the properties of a rock, as sand is just small stones, he gained a form not unlike Marvel's Sandman. A being comprised of small grains which he can manipulate in a variety of ways.