Illyana is a study in contradictions. On the one hand, she's very like the six year old child who was pulled into Limbo - the thing she wants most is to fit in and be loved. She's desperately loyal to her friends, and will do anything for them. Despite her unusual upbringing (which she plans to keep secret), she is determined that no one is going to know there's anything unusual about her.
Unfortunately, she has no idea how, and her moral sense is skewed, at best. That she would do anything for her friends isn't an overstatement; as evidenced from her history, she would. People she doesn't like? Well, she really doesn't care what happens to them. She tends to lack any concept of the big picture, and will act on a whim without considering the consequences. Having been tossed about as a tool of other people's agendas, power is a huge temptation for her - both for itself and in the hope that it will give her control of her own life.
Illyana is fully aware that she's not normal. She knows that 3/5 of her soul is tained; she struggles to control her darker impulses, but she does it for the people she cares about, not because she's convinced it really matters. Left to herself, she would surrender to her dark side. In fact, she's pretty sure it's inevitable - she may not be the best student, but she realizes that 3/5 is a better than even chance it's going to happen anyway. It's just a matter of when.
Illyana possesses the mutant ability to control the stepping disks that link our dimension to one she terms Limbo. Stepping through these disks enables her to teleport through space and/or time via an alternate dimension. Additionally, she is able to summon a disk to send someone or something else into Limbo, although they remain trapped there until such time as she retrieves them. Her control over her power is somewhat questionable, and the greater distance she attempts to transverse increases the likelihood of her reappearing somewhere, or somewhen, other than when she intended. In addition, such factors as fatigue or distress will cause her to miscalculate.
Illyana is also a powerful sorceress, having served several years as apprentice to first Ashake, then Belasco, a sorcerer and devotee of the Ancient Gods, who attempted to corrupt Yana so as to open a portal to give his gods (and himself) full access to Earth. Her powers are limited on Earth, and primarily manifest through her Soul Sword, which has the ability to dismiss spells and injure or kill demons and other magically based lifeforms, though it will pass harmlessly through anyone else. As a side effect of her mystical abilities, it is virtually impossible to probe Illyana telepathically.
Illyana is fluently bilingual in both English and Russian, and can read several archaic languages due to her studies of ancient spell books. She's also a talented fighter, especially with a knife or sword.
Pop culture, fashion, music - in other words, anything she feels she "should" know and doesn't. She knows a great deal about magic, and enjoys mocking shows that portray it inaccurately.
Illyana was born in the rural community of Ust-Ordynsky, Russia. Younger than her siblings by nearly a decade and the only girl in the family, Illyana never lacked for love and security. Until, that is, she was six years old. Outside alone, she heard a voice calling her name and followed it. And fell, almost literally, into Hell.
More accurately, Illyana was lured into a stepping disk that transported her to Limbo, a demonic dimension that serves as a nexus of time and space. There she was greeted by Belasco, the ruler of the domain, who sought to use her as a gateway by which the Elder Gods he served could reach Earth. Towards that goal, he pulled forth a bit of Illyana's soul, warped it, and created the first of the Bloodstones, which he put into what he referred to as the Beatrix amulet. When all five bloodstones were in place, he explained, the gods he served would be able to use Illyana as a portal to reach Earth.
Fortunately for Illyana, before Belasco could corrupt her further, she was stolen from him by his former apprentice, now an elderly woman who'd turned her back on Belasco's evil and escaped to Earth. Ashake tried to undo what Belasco had done, and when she proved unable to do so, she took Illyana as her own apprentice, hoping to diminish Belasco's influence. She taught Illyana for a couple of years at her coven in Salem, and Illyana had a relatively normal life for a while, attending school and learning the basics of magic. After a while, Illyana almost managed to forget what had happened to her in Limbo.
It didn't last. While Belasco's influence on Earth was minimal, he was able to track Illyana through the piece of her soul that he'd corrupted. His minions ultimately found her and pulled her into Limbo - along with Cat, a young friend of Ashake's who had her own history with Belasco. The next few years were spent on the run, and while Illyana didn't receive any traditional education, she learned a lot about defending herself, about living off what she and Cat could find, and about fighting.
Until Belasco caught up with them. As his first act, he warped and twisted Cat into a demonic version of her namesake, forcing Illyana to watch. As his second, he handed the now 12 year old girl a knife. It called to her, magic to magic, offering power - and using it, she formed the second bloodstone herself, and took her place as Belasco's apprentice.
Two more years passed. Illyana learned everything she could from Belasco, gaining power and knowledge while planning to turn against him once she'd acquired the necessary skills. Belasco was a far harsher taskmaster than Ashake had been, and Illyana's studies were punctuated with punishments and reminders, most of them administered by Belasco's chief demon, S'ym. Eventually, her mutant abilities manifested, and Illyana learned that she had the ability to call and manipulate the stepping disks that occurred naturally in Limbo - no doubt the reason Belasco had wanted her in the first place. She made one attempt to reach Earth - and learned that no time had passed there while several years had passed in Limbo. Thus, her parents rejected her, unable to accept that she was the child they'd lost.
Disheartened, she returned to Belasco - and found that Ashake was once again battling Belasco on her behalf. Belasco ordered the now transformed Cat to attack Ashake, and in an attempt to save one friend and mentor, Illyana was forced to kill the other.
Unfortunately, Ashake was badly wounded as well, and when Belasco moved to strip Ashake's soul from her and offer it as a sacrifice to his gods, Illyana did the only thing she could for her - she killed her as well. Angered, Belasco formed the third bloodstone and then banished Illyana to the wilds of Limbo, assuming she'd repent and return. Instead, she called a stepping disk and teleported back to Earth. Professor Xavier registered the use of her mutant ability, and once he located her (with difficulty, given her natural defenses against telepathy), he offered her a spot at the school. With nowhere else to go, Illyana accepted.