Skin Walker

A Skin Walker, also known as a "yee naaldlooshii", is usually a person with the supernatural ability to change their form into either an animal or another human being. Being very similar to Werewolves, and other paranormal shape changers, most skin walkers abilities are largely powered by dark ritual, and the breaking of native taboos (Such as cannibalism, incest and murder, especially of family members) or are heralded to create them. Each tribes' version differs in details. Most Skinwalkers are differentiated from their brethren by being able to take multiple shapes, but are not free-form shapeshifters. The myths usually describe them as humans who wear only an animal skin, or an abomination of human and animal forms.

Primarily detailed in many Native American tales, these entities are sometimes portrayed as either practicing witches, or aspects of the trickster deity (Coyote) or something worse, from the shared mythology of many indigenous American peoples, Skinwalkers are considered one of the most fearsome monsters from Native American Mythology. In those myths, they have a few extra powers, including Telepathy, Voice Changeling (mimicing animal and human sounds) and the creation of poisonous/disease ridden "Witch Powder" or the Evil Eye. Some cannot fully shift into their animal forms and have a deformity (awkward gait, over-sized feet, etc.) revealing their true nature.

Killing one is either simplified to accusing the creature in public while in human form (which robs it of power and it dies in 3 days) or an involved, lengthy ritual.

Related to Voluntary Shapeshifting, Magical Native American. See also Our Werebeasts Are Different. Of late, it's been connected to Berserkers and more often than not, used as a shorthand by writers for "American Werewolf."

Anime and Manga

 * In the anecdotes of Saint Seiya: The Lost Canvas, there are the Beast Warriors.

Film - Live Action

 * Werewolf (1996) purports to be a skinwalker, instead of "the white man's Werewolf." No, it's the white man's werewolf, complete with silver bullets.
 * Same as the film Skinwalker (2006).

Literature

 * Part of the Navajo cultural background of some of Tony Hillerman's Leaphorn and Chee mysteries, particularly the novel Skinwalkers.
 * The protagonist of the Jane Yellowrock series is a skinwalker of Cherokee descent. The first book is, appropriately enough, called Skinwalker.
 * A skinwalker appears in The Dresden Files novel Turn Coat. It mentions the classic version, the human witch, but also mentions the entities which teach them the trade: quasi-divine beings that grow more powerful the more they are feared and have an innate ability to know how to cause the maximum suffering in their victims. Gets into a Crazy Awesome Shapeshifter Showdown with Listens-to-Wind (who kicks its ass in a manner most righteous) at the end of the book. The book also presents an alternate method of killing a skinwalker: point-blank nuclear annihilation.
 * The TV Show also had a Skinwalker -- which literally stole skins to assume its new forms.
 * Mentioned, but never seen, in the Mercy Thompson novels. They are evil shamans who wear the skin of an animal to assume its form, and spread disease and death.

Live Action TV

 * An episode of Smallville has another Wolf-shifter named after these creatures, but...yeah. Not really.
 * Lost Tapes devotes an episode to it, and it is chilling, and surprisingly accurate to the legend.
 * Skinwalkers are brought up in True Blood among the "Shifters" who can change into animals they have touched. The rumor amongst them is that they can take a human's form if they kill the person in question, becoming a skinwalker.
 * Skinwalkers also show up on Supernatural as people who can turn into various dogs and can be killed by silver.

Western Animation

 * When a werewolf-like alien appears on a reservation in Ben 10, the "Yendaloshi" is mentioned repeatedly.