"Sylvia Engel", along with her "siblings", was implanted with false memories that resulted in a strong grudge against X-Force who, as they believe, was hired by some pharmaceutical company to kill their father who discovered a cure for autoimmune diseases, and that the Omega Clan had been helped by a benefactor to take down the mutant strike team.
When Wade Wilson tried to infiltrate the White Sky facility, he was discovered and battle the Omega Clan released on him. He quickly backed up by fellow X-Forcers Wolverine and Nightcrawler, and both of them were tortured by the three clones, until Deadpool managed to stop them by sending his own White Sky creation: Alpha Achromic.
When X-Force infiltrated the base, Omega Black was the one along Daken and Blob to stop Deadpool while he was trying to exfiltrate Evan. After being captured, Wade was inspected by Sylvia in order to remove his telepathic dampening device, and once Farouk had probed his mind, Omega Black was asked to kill Wade by filling his head with cancer, but she intended to finish the work by beating him up, using a wrench.
She stopped as she was asked to bring Evan to see Wolverine drowning, in order to push him to wear the Celestial Armor and ascend as Apocalypse. As Daken was beating him to death to make him reveal his nature as Wolverine was dying, Omega Black stopped him and brought the boy back to the torture room with Deadpool, and then left, while Evan wore the Celestial Armor to end this.
Omega Black became a vessel for Shadow King which the Crimson Pirates were supposed to give to Tullamore Voge. Bloody Bess used a psi scan on her and accidentally released Shadow King and infected The Crimson Pirates all except Bloody Bess.
House Of X
Omega Black alongside the rest of the Omega Clan was eventually invited to the new mutant island of Krakoa, created by Xavier, Magneto, and Moira X in order to heal mutantdom and start over as a whole species together.
Powers and Abilities
Disease Release: Using her tendrils, she can affect people with such disease as cancer.
Omega Black's chest is implanted with five retractable Carbonadium tendrils.
In Uncanny X-Force #34, Omega White's vegetative body became the Shadow King's prison. In Nightcrawler (Vol. 4) #8, Omega Black's body housed his consciousness. This may just be a mistake on the part of the writer.