Shapeshifting

Shapeshifting is the practice of magically altering one's physical appearance. It may be presented as voluntary or involuntary, by means of either a curse or intentional magical works.

Cryptids
Shapeshifting is a common theme among various cryptids, including:
 * Fleshgait can mimic the appearances of others
 * Skinwalker changes between human and animal forms
 * Werewolf
 * Therianthropy

External sources

 * M.T.H.O.S. by William R. Wraithe purports to have knowledge of how to shapeshift.
 * The Shifter's Bible is a successor to M.T.H.O.S. with techniques for instantaneous shapeshifting without long periods of programming one's "morphogenetic fields".