An arena packed with beauty queens... I'm scared to go in there.
Circe is a very prideful and self-centered woman. She believes herself to be the most powerful magical being and openly mocks her opponents whenever she is capable of overpowering them. Since she places such importance in herself, it is only natural that she becomes very scornful and vengeful should anyone damage her pride; the most notable victims of this being Scylla and Charybdis after the latter rejected Circe due to already being happily engaged.
#104: The Mirror of the Sea
Circe makes an appearance more than halfway into Issue 104 in a flashback of Scylla's as Musa explains hers and Charybdis' curse to the Winx. According to what Scylla had told Musa, she and Charybdis lived in a small village along the coast and were only but a few days from their wedding day, however, the two lovers soon fell victim to a curse from the scornful witch. Apparently, Circe was also in love with Charybdis and she turned him and Scylla into horrible sea monsters when she was rejected by him. Due to their new forms, the two lovers were exiled from their home into the depths of the ocean, where they have been unintentionally terrorizing sailors for millennia.
Musa continues to explain that the two have been searching for Circe's home to get her Mirror of the Sea hoping that it could change them back to their human selves. Having heard all of this, the Winx ultimately agree to help Scylla and Charybdis and head for Circe's Island for the Mirror.
A short while later, the Winx and Selkies arrive at a small island with nothing but an abandoned lighthouse. After being told by Phylla that certain rumors of that lighthouse being haunted have been spreading, the Winx deduce that Circe resides somewhere within it and promptly search the inside of the lighthouse for her Mirror.
Once inside, the Winx are quickly led down to the basement by negative energy readings courtesy of Tecna's device, and the six fairies find the source of the negative energy: a golden statue of a woman holding a plate. Aisha quickly notices that the plate looks like a Mirror and, after seeing the glass of the Mirror act like water, she concludes that it is the Mirror of the Sea as she snatches it. Unfortunately, her act of taking the Mirror causes the statue of the woman to crack apart and reveal that it was really Circe.
Awoken from her long slumber, Circe demands to know the identity of the culprit and, upon seeing the Winx, springs into battle while threatening to turn them all into monsters. Bloom reveals that they have already taken the Mirror of the Sea, meaning that she will not be able to do so, but that does not stop Circe from duplicating herself to confound them. To help identify the real Circe quickly, Musa whips out her Diapason to torture Circe's eardrums. The unbearable noise produced from her spell causes Circe to writhe in pain as her duplicates crumble, however, she quickly retaliates with a powerful blast of magic that even Flora could not block!
With Flora, Musa, Aisha and Tecna down, Circe flies outside to take care of Bloom and Stella, only to be surprised by the two of them being at the highest point of the lighthouse with the Mirror. Things only go from bad to worse for Circe once Scylla and Charybdis emerge from the shore waters and Stella, using her power over light, uses the light reflected in the Mirror of the Sea to reflect what is really in the hearts of Scylla, Charybdis and Circe. This causes Scylla and Charybdis to be turned back into humans while Circe is transformed into a shellfish.
With Scylla and Charybdis saved, Bloom looks for Circe to see where she ended up, only for Stella to show her that she had been turned into a tiny shellfish. Circe pinches Stella's finger in retaliation for her teasing but, with her new form, she will no longer be a threat to anyone.