The Soulsword was created by Illyana Rasputina during the period in which she was trapped in a Limbo dimension ruled by Belasco. Illyana magically caused her own life force energy to manifest before her. Once this happened she cast her hand into the eldritch energy and drew from it the Soulsword. A simple looking blade upon its origin, it began to develop intricate designs and forms upon itself the more Illyana used it, becoming more powerful with each use. Although usable as a physical weapon, its main use is to disrupt magical spells and beings, usually permanently. It was accompanied by armor covering Magik's left shoulder, chest, and arm. Control of the Soulsword seems to guarantee mastery over Limbo, but its full power could only be accessed by Magik. When Magik reverted to six years old, the sword transferred to her best friend Shadowcat.
Mystic Right: The Soulsword is a physical manifestation of Magik’s magical powers as well as the limbo dimension she rules. As the Soulsword is the living embodiment of Illyana Rasputin, whmoever owns the sword is considered to be the ruler of Limbo (Otherplace) just as Illyana once was. Only the ruler of Limbo can weild the sword and only the wielder of the sword can rule limbo.
Strike the Supernatural: The Soulsword has been shown to only harm magical creatures or objects -- it rarely injures non-magical beings or items.
Maim the Ethereal: Intangible and ethereal beings can also be struck, as Shadowcat painfully learned.
Counter/Break Spell: When Magik uses the Soulsword to strike a person who is possessed, ensorcelled, or otherwise magically controlled or transformed the sword will be able to counter or break the spell.
Stepping Disc Control: The Soulsword can be used to control Limbo's 'stepping discs.'
Spell Sword: Jimaine has learned to 'draw' spells with the sword using arcane symbols.
Sword Summoning: Magik can store her Soulsword in nothingness and summon it whenever she desires.
Summon Armor: It can also be used to summon promethium battle armor around the wearer.
Augment Magic: Any magic user who holds the Soulsword instantly has their mystic abilities augmented.