Cassandra Nova is a fictional supervillain appearing in American comic books published by Marvel Comics, most commonly in association with the X-Men. Created by writer Grant Morrison and artist Frank Quitely, Cassandra first appeared in New X-Men #114 (July 2001). Cassandra is a "mummudrai," a parasitic life form born bodiless on the astral plane. The mummudrai that became Cassandra became telepathically entangled with the future Charles Xavier, who possesses vast mutant telepathic powers.

Now in Xavier's body, Cassandra mentally forced the Xavier Institute student Beak to beat Beast into a coma after he discovered that Xavier and Cassandra shared the same DNA. Cassandra Nova then contacted the Shi'ar, whose leader was Majestrix Lilandra, Xavier's lover. Cassandra manipulated the Shi'ar Imperium, driving Lilandra insane and using her to make the Shi'ar Imperial fleet destroy the empire. Cassandra also made Lilandra send the Shi'ar Imperial Guard to wipe out the mutant population of Earth, starting with the X-Men. The Guard fought the X-Men until they were able to show the truth to the Imperial Guard.  Angered at Cassandra's treachery and realizing the danger she posed, the Imperial Guard fought Cassandra, who defeated them and headed into the mansion. She had planned on using Cerebra to eliminate all mutants. However, Jean Grey (who was becoming increasingly powerful due to a manifestation of the Phoenix entity) was able to split Xavier's consciousness into pieces and store a little part of him in every single living mutant mind. When Cassandra used Cerebra and focused on all the mutants, the pieces of Xavier's mind were brought back together; at the same time, Jean Grey telepathically attacked, successfully defeating Cassandra, and forcing her out of Xavier's body.  Without a body, Cassandra became pure psychic energy, bodiless and blind. Emma Frost tricked Cassandra into returning to what appeared to be her old body, which was in reality the alien polymorph "Stuff." Cassandra's essence entered the body and was locked into a self-repeating program in the synthetic brain.

was this successful?
The Guard fought the X-Men until they were able to show the truth to the Imperial Guard.