Originally Posted by
sunofdarkchild
There's the OG Claremont version and the modern post-resurrection version. I suppose you could have 'sub-versions' like Simonson, Wells, Bendis, ect. But I wouldn't classify them as separate versions. And I don't consider any of the alternate reality versions, like Age of Apocalypse or Exiles, to be 'main' versions.
The 2.0 Illyana has gained the wisdom of experience and has gained a level of confidence and control Claremont's never had. The duality is still there, but it is lessened. She has fully accepted who and what she is and is and usually faces problems head-on instead of running away like she used to. She is snarkier and seemingly nastier, but in a way has more empathy and able to see herself in others with her greater experience. The danger of her falling to the dark side if she loses control is still there, but it is greatly lessened from her less mature days. As a result she can go to extremes she couldn't have before and not risk losing control.
As for her power levels, the difficulty is that every version of her holds back the vast majority of her power almost all the time. At her best, in full-darkchild mode in Limbo, she is a reality warper. As a Hell-lord, she has status similar to the likes of Mephisto. Amanda Sefton, who has been stated to be weaker than Illyana, scared Mephisto. And later Illyana defeated Dormammu. At her absolute best in Limbo she is probably well above Dr. Strange.
But she rarely uses that power. It is dangerous, and most of the time it is also overkill. Plus she hates it. Even in her more mature incarnation, it is only with great reluctance or in moments of overwhelming anger that she resorts to it. If she ever truly falls, the X-Men as a whole have no chance against her unless they have the Phoenix on their side at full power. She will corrupt some of them to her service and kill the others while making it look easy. At that level only something with a cosmic level of power like the Phoenix stands a chance against her.
Below that is her regular sorcery. In Limbo this is sorcerer supreme level, while on earth it is inconsistent, where she can sometimes cast spells and sometimes can't, depending on the story needs. Since Bendis had her learning under Strange she has been able to cast spells on earth more consistently, but not at sorcerer supreme levels.
She created the soul sword, one of the most powerful mystical artifacts in the entire Marvel Universe. With the sword-fighting skills she learned training with Cat, she can use the sword instead of her spells, in effect holding back even more. But with her skills and the sword's power, she is capable of fighting evenly with mystically based foes on the level of Thor.