I've noticed on this thread that all the ideas everyone had-are creatures we all know quite well, or very close anyway. Why not create your own
unique creatures right from scratch? (You could still base it off a...earthly creature.) You can make dogs and spiders, etc... fine, so I'm sure you could make your own. Not to mention it adds to the creativity of the game. Creatures seem much more believable (I spelled it right!
when you never seen it before, or anything simular to it. (You may notice this when it comes to robotics)