Some myths explain Scylla's beginnings. One of them says she was one of the daughters of Phorcys the Greek God of the Deep. Another says that Scylla was a very pretty fairy who was liked by Poseidon, but the jealous Amphitrite turned her into a monster by poisoning the water of the place where Scylla would swim.
One says that a jealous Circe poured a potion into the sea water and then made Scylla transform into a monster with four eyes and six long necks with ugly heads. Her body had 12 tentacle looking legs and a tail. She attacked the ships of nearby people.