Scylla was an ancient demon that resided in Infernus and shared a symbiotic relationship with another demon, Charybdis, whom acted as her mount. She served Satan in ancient times, and in more modern times (namely the Mythic Dawn War), she and her mount served Overlord Laharl as a battle commander in the war against Earth.
She was a very high ranking demon, surpassed in rank only by the Pit Fiend, King Antroklis, Laharl, and Satan. She is extremely powerful, having the power to command her massive beast of burden, Charybdis, and able to unleash terrible powers capable of huge damage. Though she is very powerful, she only is active when called upon. Otherwise, she spends her time hibernating and gaining power.
During the Mythic Dawn War, she was summoned by name at the request of Laharl to serve him and Veigar in the Mythic Dawn's crusade against Earth. She and Charybdis assisted the Dawn in destroying the Earth. She, along with Antroklis and the Pit Fiend, led the forces of Hell in the war, and she herself is responsible for the deaths of many people, among them being two of the last members of Blue team: Kamina and Mewtwo. She eventually met her end at the hands of Lucario wielding the Godblade.