Common between all the sets are lots of the new ball-hinge parts, as well as many other clip joints. All the characters also seem to have big googly eyes, either printed on balls, or round plates. Teeth and claw parts are also quite common, along with more unusual and visually distinctive parts such as flames and lightning.
The first wave of nine sets includes three sets of three characters which appear to be based on fire, rock, and electricity. The three sets for each element can be combined to create a larger character to represent each theme.
Here are the sets in wave one (packaging images via Hoth Bricks), the guide continues after the jump:
Here's a page from a Lego catalogue, illustrating how each of the three characters for an element can combine into a larger design: