SHI'AR IMPERIAL GUARD versus
Superdestroyer (Marvel comics)
Where: New X-Men #124 When: May 2002
Why: Grant Morrison How: Igor Kordey
The story so far...
Cassandra Nova, a malicious Shi'ar mummudrai, had her first encounter when drawn to arch-nemesis Charles Xavier in the woom. There, Nova duplicated Xavier's DNA to sustain a physical form, but with his mutant fetal brain developing in fantastic ways, Xavier became aware of the creature's viciousness and attacked, resulting in the Xavier twin being stillborn.
Decades later Nova would set into motion plans to annihilate all that her "twin" held dear. It would be Nova that would set off events that decimated the mutant nation of Genosha, before facing Xavier and his X-Men herself, taking possession of her nemesis' body before her own was crippled, thus leaving Xavier in the incapacitated body.
Under the guise of Xavier, Nova continued her scheme to destroy Xavier, linking up with Lilandra of the Shi'ar to convince her the mutants had become infected and would need to be destroyed for the good of the universe. Thus, Lilandra reluctantly sends her army to Earth, where they descend upon the X-Mansion.
Full Article: http://secretearths.blogspot.com/2007/08/shiar-imperial-guard-versus-x-men.html