Reddit mentions of Fantasy Creatures in Clay: Techniques for Sculpting Dragons, Griffins and More

I bet you are more interested in people than animals but this book was extremely helpful in teaching me how to make the kinds of sculptures you are talking about. It goes into everything you need including how to make armatures, materials, the 'sculpting' part, textures, how to paint a sculpture, etc. The look inside section gives you a good idea of what it's like, and note that there are tons of pictures of all of the techniques it talks about. It's designed to generalize to lots of different creatures - more about giving you the guidance to make your own things than telling you how to make a specific sculpture.
It does not talk about molding, so you'll have to find a different reference for that.