The younger sister of the X-Man Colossus, Illyana came to live with her brother after being kidnapped by the eccentric assassin Arcade. Months later, the sorcerer Belasco captured Illyana and held her prisoner in the pocket dimension Otherplace, a.k.a. Limbo. Belasco turned a portion of her soul demonic in nature, and in the process conjured a “bloodstone” gem from her soul. When Belasco conjured five such gems, Illyana, who would have transformed into the entirely demonic Darkchilde, would serve as the means by which Belasco’s demon masters, Chthon and the N'Garai, could conquer Earth.
Belasco’s spell gave Illyana considerable magical power, and she nearly killed him, but decided not to give in to her demonic side and drove him from Otherplace, becoming its new leader. Illyana returned to Earth at a point only seconds after the X-Men’s escape from Otherplace. However, whereas only seconds had passed for the X-Men, Illyana had aged seven years in Otherplace and was now 13 years old. She then joined the team of superhuman mutant trainees the New Mutants as Magik.
(copied and pasted from Marvel Universe)