Shapeshifter/Fablehaven

Skinwalkers are humans that have the ability to shapeshift into an animal. During the excursion to Painted Mesa at the Lost Mesa preserve, Neil transformed into a chestnut stallion in order to transport Kendra and Gavin to safety. Neil said that shapeshifting was draining, so potentially, Skinwalkers can be exhausted by transforming into an animal. They seem to be similar to Shapeshifters.
In mythos, Skinwalkers are said to be created by commiting an extreme crime(ie; murdering one's own family) with intent to become one as a result, and are usually more animal like than in Fablehaven. Though if this is true in the Series is unknown, though offspring of Skinwalkers usually gain the same powers in legend, so it is possible that this is true.