Cryptids, you say? What about the Thunderbirds? 8)
http://cryptidz.wikia.com/wiki/Thunderbird
EDIT Or kitsunes? Or maybe witches?
The wiki article for shapeshifting does say: "The idea persisted through the Middle Ages, where the agency causing shapeshifting is usually a sorcerer or witch, and into the modern period." So maybe a sorcerer? (Source: https://en.wikipedia.org/wiki/Shapeshifting )