Officially, they're called "cryptids." The term comes from cryptozoology, the study of animals that the researcher believes are real, but for which there is little if any conclusive proof. Some folks swear they exist, others scoff at the mere mention of their names.
And you've heard those names, at least some of them. Bigfoot. The Jersey devil. El chupacabra. Nessie. Well, now you can do more than just hear of them. Now you can use them in your games. Classics of Controversy is the latest in Lion's Den Press' popular Iconic Bestiary line, and it provides you everything you need to introduce fantasy variants of these creatures into your campaign.