Mestra (Μήστρα) was the daughter of King Erysichthon — cursed by Demeter with insatiable hunger. She was given by Poseidon the power to shape-shift, and her father sold her over and over to buy food; each time she returned to him in a new form.
Featured in Ovid's Metamorphoses Book 8.
Mestra reduces to three — the number of Greek shapeshifter.