Cassandra Nova is a very powerful enemy of the X-Men and also one of their more recent ones, though her origins go back as far as the birth of Professor Xavier himself - a member of a parasitic race of psychic beings Cassandra attached herself to the unborn Charles Xavier while still in the womb, in essence becoming his twin sister but also embodying the darkest parts of Xavier's mind.
Becoming aware of her presence - and the threat she posed to the world - the infant Xavier seemingly vanquished Cassandra before even being born but somehow she would survive and grow mad, becoming convinced that she and Xavier were the only real things and that everything else was a lie.
Cassandra was also deeply weakened from the battle with the infant Xavier and it took her years to reform to a level of power suitable to become a threat to the X-Men, her most infamous act of villainy was when she commanded an army of Sentinels to mercilessly massacre over 16 millions mutants on the island of Genosha - making her one of the most destructive villains of the entire series (at least in the mainstream reality).
Cassandra Nova is not content with this massive lose of life though and is still planning more mayhem, being described as Xavier's dark half personified, seeking destruction and genocide so that she may accomplish what she sees as her true goal in life: to erase every "illusion" Xavier holds dear.
Cassandra 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 Charles Xavier, his mummudrai was able to create a physical form, effectively a twin. While gestating in her mother's womb, Cassandra was recognized by Charles as his evil alter ego, and he preemptively tried to kill her with his nascent psychic abilities. Cassandra was barely able to defend herself, and the shock of the roiling battle caused a miscarriage of Cassandra's fetus. 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.
When she emerged, Cassandra located a secret "wild" Master Mold in the South American jungles that was able to adapt existing technology into a wide variety of lethal Sentinel forms. She convinced a cousin of Bolivar Trask to accompany her to the Master Mold, where his voice activated the control protocols. After killing Trask by merging herself into his body, she dispatched giant Sentinels to Genosha, resulting in the genocidal massacre of over sixteen million mutants, including Magneto. Her Wild Sentinels also attacked the X-Wing, downing it with Cyclops, Wolverine and their passenger Ugly John aboard. The X-Men subdued Nova, but lost Ugly John. Wolverine severed Cassandra's vocal cords and she was brought to the Institute, where she began to exert telekinetic and telepathic control over the X-Men, making her way to Cerebra by phasing in an effort to destroy all mutants. Then Emma Frost snapped her neck, stunning Cassandra, who was finally put down by six gunshots from Charles.
What no one realized at the time was that just before the shots, Cassandra switched her mind into Charles's body and vice versa. Using Charles's form, Cassandra "outed" him and the X-Men to the world, then left Earth with Lilandra for a "vacation." While in the Shi'ar Empire, Cassandra used her powers to take control of the Imperial Fleet and began to destroy the Empire. Lilandra made for Earth, but Cassandra destroyed the ship, and upon arrival back at the Institute took down the Superguardians as well. By this point, Cassandra (in Charles's body) had constructed a psychic monster around herself, seemingly made up of the flailing body parts of all the people she had absorbed or controlled.
After beating off all comers, Cassandra again came to Cerebra. She tried to use Cerebra to access the minds of all Earth's mutants, but Charles's mind was waiting for her (put there by Jean Grey) and he forced her out of his body. Formless and with no life support, Cassandra flailed about until Emma came in with Cassandra's body, which the entity entered, only to be trapped inside, as her real body was dead, and this body was the Imperial Superguardian shapeshifter Stuff.
Nova is now trapped inside Stuff. Her mind has been blanked and she is being re-educated by mental simulcra of Professor X and Phoenix. It appears that she was allowed to take the form of the "super-strong" girl Ernst while she underwent her re-training, which may explain why Ernst always carried along the disembodied brain of Martha Johanssen - Martha was probably performing the telepathic re-education on an ongoing basis. Ernst was part of the Special Class, for a time until it reformed for a time into the Brotherhood of Evil Mutants. However, it should be noted that Cyclops and Beast did not know about this transformation, and it is uncertain whether Xavier himself did.
Cassandra (back in her original form) returned, alongside Sebastian Shaw of the Hellfire Club.
So far, it has been revealed that she used her vast psionic powers to awaken Emma Frost's Secondary Mutation which granted her the ability to turn herself into "living diamond" in exchange for the favor of Emma infiltrating the X-Men. Hints are also given that Emma in return did something more for Cassandra. Its also been revealed that the new Hellfire Club was Nova getting into Emma's mind and using her telepahtic powers to create the illusion that the Hellfire Club was there.
Powers and Abilities
Cassandra possesses telepathy comparable to Charles Xavier. After copying the DNA of Charles Xavier, the mummudrai Cassandra Nova accessed the full spectrum of latent mutant functions in his genome (this means she has the powers of Charles Xavier, the ones he could have had and the ones he might receive, as a result of latent mutation), granting itself vast psionic powers. These powers include: telepathy, telekinesis, and the ability to release an astral form, which she focuses both her telepathy and telekinesis. She has all the powers of the "average" mummudrai as well.
DNA Duplication: able to copy the DNA of sentient beings and use it to construct physical bodies for themselves. Also capable of accessing the full spectrum of latent mutant functions in ones genome.
- DNA Manipulation: can manipulate the DNA of others, breaking it down at the molecular level.
- Jumpstart: After analyzing the DNA of another superhuman mutant, Cassandra is able to selectively evolve their existing genetic traits as well as catalyze the untapped genetic potential of latent mutants. Once begun, the procedure is irreversible and can often result in unpredictable side effects.
- Phasing: ability to pass through solid matter by passing her atoms through the spaces between the atoms of the object through which she is moving. In this way she and the object through which she is passing can temporarily merge without interacting, and each is unharmed when Cassandra has finished passing through the object. This process is called “phasing.” When Cassandra is phasing she is intangible.
- Metahuman Regeneration: She regenerates and heals hundreds of times faster than a normal human. Thanks to this superhumanly regenerative "healing factor," she has been able to completely recover from injuries which would prove fatal to most humans, even those with superhuman abilities. She can regenerate organs such as eyes or large portions of flesh, regenerate limbs, such as feet and arms, which have been completely severed.
Astral Form Projection: ability to release her astral form, which she uses to focus her telepathy and telekinesis.
- Telepathy: can read minds and project her thoughts into other minds within a vast, potentially limitless radius.
- Telepathic Cloak: Can mask her presence from being detected by others. Her abilities can at times go undetected or be counteracted by other more powerful telepaths depending on their level of skill in using their own psi abilities. She can extend these defenses to others around her as well.
- Mind Control: ability to control the minds of others upon mere concentration.
- Mind Possession: ability to possess the mind of another, and use that beings body as your her own
- Mind Alteration: ability to alter the minds of others by force of will.
- Psionic Shield: ability to erect a psychic shield for protection of herself and of others minds
- Telepathic Illusions: ability to create illusions to make herself seem to be invisible, look like someone else, or make others experience events that are not truly happening.
- Mental Paralysis: ability to induce temporary mental or physical paralysis
- Mental Amnesia: Can erase any awareness of particular memories or cause total amnesia.
- Psionic Blasts: can project psionic force bolts which have no physical effects but which can affect a victim's mind so as to cause the victim pain or unconsciousness and turning someone brain-dead.
- Astral Projection: can project her astral form from her body onto astral planes or the physical planes. In the physical plane she can only travel in astral form over short distances. In the astral plane, she can mentally create psionic objects and manipulate the aspects of her environment.
- Mind Transferal: able to transfer both her mind and powers into other host bodies should her own physical body be somehow killed
- Mental Detection: can sense the presence of another superhuman mutant within a small but as yet undefined radius of herself by perceiving the distinctive mental radiations emitted by such a being.
- Telekinesis: possesses telekinetic abilities enabling her to levitate and manipulate living beings, inanimate objects, and to some extent energy psionically. She can levitate herself or other persons or project a telekinetic shield capable of withstanding missile blasts. By focusing her mental energy at a specific target, she can release devastating force blasts