Complex sentence: In mythology, folklore, and modern fantasy fiction, shapeshifting is the ability of a being able to physically transform into another form or being, either as an inherent faculty of a mythological creature, or by means of magic.
Split into simpler sentences: In mythology, folklore, and modern fantasy fiction, shapeshifting is the ability of a being able to physically transform into another form or being. By transofrming someone can either form as an inherent faculty of a mythological creature, or by means of magic.