GENOSHA: Revenge of the Acolytes
Cassandra Nova Xavier is what the Shi’ar call “Mummudrai”, the spirit that is the equal and opposite of a person. However, due to the amazing genetic potential of Professor Charles Xavier, his Mummudrai was able to create a physical form, effectively a twin. While gestating in her mother, Sharon Xavier’s, womb, Cassandra was recognized, by Charles, as an evil presence, and he pre-emptively tried to kill her, with his nascent psychic abilities. Cassandra was barely able to defend herself and the shock of the roiling battle caused her miscarriage. Though the doctors pronounced her stillborn, Cassandra in fact survived and spent the next thirty-plus years as a growing mass of cells in a sewer, building a new body for herself and planning her revenge on her brother.
Cassandra spend further decades regrowing and taking human form. She sought multiple times to destroy the X-Men, using her incredible telepathic powers to manipulate or destroy those in her way. Yet her brother Charles always managed to fend her off. In one such encounter, Eric Lehnsherr came to the aid of his old friend against Cassandra, nearly killing her in the process. Cassandra survived and turned her attention on Magneto. She manipulated Senator Kelly and others into launching a full-scale assault on Genosha. The resulting massacre killed thousands of innocent civilians, leaving the bastion of peace in ruins.
Cassandra immediately vanished following the attack, leaving the Genoshans to wonder if she will return to finish her vendetta.