Mestra is not really a goddess, can shape-shift very easily and at will. She got granted this power by Poseidon, her lover. She is the daughter of Erysichthon of Thessaly, and her father attempted to sell her from her powers, gaining him a large amount of money.
Mestra is good at acting, and can pull on an act. She is described as "two-faced".
Mestra can shape-shift at ease, much easier than Iris.
Mestra's official Greek name is Μήστρα.