Medusa was a one time character from Hi Hi Puffy AmiYumi. She is a precursor of Harmony.
Medusa only appeared in episode, The Golden Fleas. She was a purple gorgon who feels like Amius's and Yumius's Numbuh One fan. Amius and Yumius tried to get Medusa to look at herself in a mirror so that they wouldn't have to look at her because they know they'll turn into stone. So Yumius suggests that Medusa look into a body of slime, Medusa does so, but she turns herself into stone and Yumius simply knocks her into the body.
Medusa's voice is just like Harmony's because of Sandy Fox.