Jenova's powers and abilities
Due to her parasitic nature and alien biology, Jenova has many abilities to spread her influence and swiftly eradicate all living beings on the planets she eventually comes across.
Infection: When interviewed by Professor Gast, Ifalna, Aerith's mother, mentioned that Jenova unleashed a deadly virus on the Cetra once they made contact. This virus is generated and stored within her own body.
Madness: Ifalna's recount of events also mentioned how the virus led people to go mad. A possible example of this could be the Sephiroth Clones, who are injected with Jenova's cells. People who lack strong willpower will become puppets of Jenova's will and lose the sense of self, beyond whatever Jenova (and later Sephiroth) may want from them. It can be speculated that the virus has similar properties to the Jenova Cells.
Mutation: The third effect of Jenova's virus, people infected will become monsters.
Enhancement: With the right procedure, and under some very strict conditions, the use of Jenova's genetic material can have beneficial effects for the host, such as greatly increased physical abilities and even replication of Jenova's other abilities. This is the result of the Project S branch of the Jenova Project, whose result was Sephiroth himself, and later a simplified replication of it in the form of the SOLDIER Program to create Shinra's army of Super Soldiers. The conditions to avoid most negative effects require using pure Jenova Cells to avoid biological decay, ensure the host intertwines properly with Jenova's material (such as in Sephiroth's case, who received the cells as an embryo) and the individual must have a strong mind so he will keep his sense of self. However, must be noted that not all negative effects are eliminated, even successful SOLDIER are potentially vulnerable to Jenova and Sephiroth's influence and the presence of the cells will make them vulnerable to Geostigma.
Shapeshifting: Jenova can easily transform and change her appearance or parts of it to take different appearances, mimic other living beings or simply assume more monstrous and powerful forms. Ifalna mentioned that this is how Jenova deceived the Cetra, by turning into their friends and family, and during the game, it can be seen how fragments of Jenova's body can transform into replicas of Sephiroth's original appearance as well as large monstrosities to fight the party.
Regeneration: Under normal circumstances, Jenova can quickly regenerate damage done to her body, including lost limbs and wounded organs. If the damage sustained is too great, however, Jenova will still survive, but will need the process of the Reunion, to heal herself.
The Reunion: Even if Jenova's body is torn to pieces, her parts, even single cells will eventually gather back together to rebuild her body, regardless of how far away they are from each other and the conditions. The name "The Reunion" was coined by a theory proposed by Professor Hojo, who first discussed this idea; carrying out an experiment by injecting normal people with Jenova Cells and observing that they had their wills overridden by Jenova and Sephiroth and had no other purpose than gathering together for their master, eventually migrating to Jenova's location. Among those people, Cloud Strife himself saw his actions influenced by this instinct caused by the Jenova cells in his body. Depending on the context in which her cells have separated the process of the Reunion may take even years, so it may or may not be combat applicable.
Geostigma: The newest effect Jenova Cells have on the host, thanks to Sephiroth's influence as well. A fatal disease caused by the cells in the body. The parasitic presence of Jenova causes an internal conflict between the cells and the patient's Spirit Energy, this leads to the body overworking itself trying to purge the cells, which causes symptoms such as physical weakness, extreme fatigue, seizures, hallucinations, depression, dark sores on the skin which emit a black pus and, eventually, death. However, the severity of the symptoms may vary from patient to patient, some may die within a couple of hours while others may simply have occasional bouts of pain. Those who die of Geostigma won’t join the Lifestream but rather will become part of the Negative Lifestream Sephiroth created. Given Geostigma injects Jenova Cells in those suffering from it, they may have their Reunion instinct awakened and are vulnerable to Sephiroth and Jenova enforcing their will through them, which the former comments on his confrontation with Cloud as "using Jenova’s will to control those with the disease and eventually take control of the Planet". Geostigma can be contracted by contact with Jenova Cells scattered in the Lifestream, direct contact with Negative Lifestream or being wounded by a Shadow Creeper, as they are made of Negative Lifestream.
Aside from the unnatural biological properties of her genetic material, Jenova possesses extremely powerful mental powers, which she can use to complement her parasitic properties when interacting with other species. Many of these abilities are seen through Sephiroth in the original game, who inherited Jenova's abilities thanks to the Jenova Project.
Masquerade: Jenova can appear to others as someone who can be found on their memories, tricking their senses and mind so she is seen, heard and perceived as that person. If Jenova does not know a person's memories, then she will be seen in her true appearance.
Consciousness Scan: Jenova can read the memories and emotions of others, as implied by Ifalna as well. Kadaj later shows Jenova could fully scan the consciousness of a person and thoroughly investigate their memories. This ability, among the other Jenova has extends to everybody who has her cells, but to a lesser extent and varying degrees.
Pain Bind: While never using this ability herself, as seen with Kadaj, Jenova can heal wounds and take away the pain of a person. However, at any time she wishes, she can reopen the wound and injuries she had previously healed and return the pain in full force to said person.
Telepathy: While mostly Sephiroth showed the ability to project his voice into the minds of others, and did so several times, Jenova, in one meaningful moment and in her single spoken line in the entire compilation, left a single message to Cloud Strife after her defeat following Aerith's death: "Because, you are... a puppet."
Mind Control and Possession: Those injected with Jenova Cells, unless they naturally have a very strong mind, will inevitably have their sense of self overridden by Jenova's own will, as seen with the mental decay of the Sephiroth Clones. However, even if they do withstand the presence of the cells in their bodies, they are still vulnerable to manipulation and active influence from Jenova or Sephiroth, who can force control of their minds and bodies to use them as puppets. The entire Reunion occurs thanks to Sephiroth Clones becoming puppets whose only purpose is to return to their masters Sephiroth and rejoin Jenova.
Illusion Creation: Seen through Sephiroth, during the encounter in the Whirlwind Maze, he displayed the ability to create whole illusory scenarios by recreating the entirety of Nibelheim down to its last detail and just moments later show its destruction, and later trick the person holding the Black Materia (Barret or Red XIII) by concealing the party and his surroundings from him.
Telekinesis: As seen though Sephiroth, Jenova had the ability to levitate people with her mind, displayed when Sephiroth managed to restrain and hurt the party in their final confrontation in the original game.
Levitation: During the final battle against Jenova, she can be seen levitating towards the party and during the fight. Before that, the parts of Jenova, taking Sephiroth's shape, were commonly seen levitating and flying while travelling from one place to another.
Intangibility: As seen with the Jenova fragment taking Sephiroth's shape in the Cargo Ship, Jenova can easily phase through solid matter. Another possible instance of this ability is seen in the encounter between a Sephiroth body and Tseng in the Temple of the Ancients, Tseng had sent a subordinate to the single entrance to the room and neither he or said subordinate had noticed anyone else in the room, then suddenly Sephiroth appeared from the opposite side, where later exploration reveals that there is only a wall.
Teleportation: Incidentally, one of the first abilities Sephiroth manifested even before he fully connected with Jenova, and likely one of the many abilities he obtained from the Jenova Project. Jenova bodies also have displayed this ability on occasion, warping small distances within the same area.
Jenova's mimic ability isn't limited to read the mind of others, she can also learn abilities and powers from the species inhabiting the planets she comes across. Such is the case with some of the spells the Cetra used, seen how Jenova learned a few of their secrets, along abilities of her own to fight directly.
Laser: A quick beam of light shot at a single target from Jenova's body. She can shoot several times in succession.
W-Laser: A more powerful variant. Jenova shoots two beams at once at a single target with enough force to create a small burst of energy. Like with the regular Laser, she can shoot several times in succession.
Tail Laser: Jenova shoots a laser and then quickly drags it through the area where the enemies are standing, creating a large explosion.
Gas: Jenova will emit this substance to attack a single enemy. Despite its name, however, it doesn't have the Poison attribute.
Red Light: Jenova causes a sudden flash of light that uses heat to strike a single enemy.
Blue Light: Similar to Red Light. However, this blue flash inflicts damage of the Water element.
Blue Flame: Jenova unleashes mystical blue fires that inflict Water damage to an opponent.
Tropic Wind: Jenova releases a searing wave of heat in the form of large red bubbles, striking an enemy with Fire and Wind damage.
Aqualung: Jenova conjures massive bubbles of water and energy at all enemies.
Bio2/Biora: Jenova conjures bubbles of venomous liquid that damage her enemies and leaves them poisoned.
Ultima: Jenova's last resort in her final battle, the most powerful black magic spell after Meteor itself. When cornered by the party, she will begin preparing this spell, indicated in-game with a countdown, and unleash it as her final attack. A massive energy wave that strikes a large area for non-elemental damage. The spell cannot be reflected.
Silence: A spell that disables the use of the voice, preventing the use of any ability that requires sound, words or vocal commands, such as Magic, Summoning, Singing, Prayers, Speechcraft, etc.
Stop: A spell that freezes the time of an opponent, effectively leaving them completely helpless.
Reflect: Casts a magical barrier that reflects all non-physical attacks at the enemy, even those which aren't specifically magic unless they have barrier piercing properties. Will activate four times before wearing off.
Cure3/Curaga: A very high level healing spell Jenova will use to hasten her regeneration.
Repeating Slap: Jenova repeatedly whips a target with a tentacle. This attack inflicts the Fury ailment.
Absorb: Jenova stings her target with one of her tentacles. This attack inflicts the Sadness ailment.
Jenova's weaknesses
The Reunion can take a long time to accomplish if her cells are scattered too far apart. Her variant of Ultima takes a while to cast unlike the one from other users. After her physical death she no longer can directly interfere with other beings despite merging with the Lifestream, and must rely on Sephiroth to do so as he kept his individuality while Jenova sacrificed hers.
