Cessily Kincaid was raised in Portland, Oregon by her parents Mark and Jill, who used to dote over her. When Cessily's powers manifested, her parents were happy that her powers had come forth and made their daughter practice using them. In response, she was sent to the Xavier Institute where she befriended Julian Keller and was placed as Laurie Collins' roommate, which led to Cessily not liking Laurie. After the school was rebuilt, she was selected by Emma Frost to be on her Hellions squad. She's extremely close to Santo Varroco and Julian Keller whom she spends most of her time with and looks upon like big brothers. During that time, she developed a crush on her teammate Wither, but her feelings were not reciprocated.
The Hellions squad won the squad challenge, and during their summer vacation, they travelled with Julian to his home. There they encountered the Kingmaker, from whom they each received a trial wish. Cessily's wish was to have her parents accept and love her, a wish the Kingmaker granted by manipulating her parents with telepaths. However, when the Hellions eventually refused a permanent deal with the Kingmaker, Cessily's parents reverted back to normal and Cessily returned to the Institute, defeated.
Soon thereafter, the events of M-Day left only 27 students with their powers, Cessily included, though she would have preferred to lose her powers and was devastated that she did not. The depowered students and staff were sent home. One bus was bombed by anti-mutant religious zealot Reverend William Stryker, and Cessily's former teammate and friend Tag was among those killed. The X-Men held a funeral for those students whose parents would not accept them, and Cessily's anguish was very visible. All of the remaining students were placed by Emma Frost into an all-out brawl, and the ones deemed to be the best were to be assigned to become a group of in-training X-Men. Cessily made the team and began training to become an X-Man.
Childhood's End and Nimrod
In the Childhood's End arc, Cessily and the New X-Men defeated Stryker, Josh killing him. Shortly afterwards the team went to help Forge who had been sought out by Nimrod for repair. During the skirmish X-23 was forced to sever a piece of Mercury's hand to separate her from Nimrod. She later commented she'd "always wanted to lose a few pounds." The team successfully defeated the robot due to combining the powers of Surge, Mercury, and X-23 and Nimrod was sent back in time.
After learning of Emma Frost's plan to have X-23 leave the school, Cessily takes Laura to Salem Center for coffee to cool Laura down. Just as Cessily realizes that Laura has feelings for Hellion, the coffee shop explodes. Facility agents led by Laura's former handler, Kimura, come for one of them. Laura, believing it is her, begs Cessily to leave, but not before Kimura shoots Cessily with an electric bullet, incapacitating her. After capturing Cessily, Kimura leaves before Laura can recuperate from a grenade blast. At the lab, Cessily questions who her captors are and what they want but is given no answers. When she replies that her friends will come for her, Kimura informs that "The Elephant" (Mammomax) said the same thing while showing a picture of his corpse in a cell. Before dying, Stryker had requested a living weapon be made, a huge beast called Predator X. Mercury's metal skin was needed to give it added powers and durability. The Facility scientists strip some of Mercury's biometal, granting Predator X her powers. The experiments leave her physically and mentally traumatized, forcing her to recuperate for some time at the Institute. She eventually regains some of her lost mass.
Quest for Magik
Mercury is recovering in bed after what happened to her in the last arc when the students are teleported to Limbo. She is held captive by Belasco but breaks free after he 'kills' X-23. She and Dust go up against Belasco and keep getting beaten down but refuse to give up, as both their mutant bodies are resistant to his magic and fight an inconclusive battle until Darkchylde and the other students arrive, teleported by Pixie. Mercury continues to fight alongside the other students, but can only watch as Belasco fends them off and proceeds to pull Earth into Limbo until he is defeated by Darkchylde and Pixie.
World War Hulk
Mercury is one of the students that intercepts the Hulk. Mercury helps in keeping Hulk pinned down in the first attack but is knocked away. When X-23 blinds him she joins in taking him down alongside Surge, Beast and X-23 but they are all knocked away when Hulk's eyes grow back. Mercury gets back up and attacks him from behind but Hulk grabs her and squishes her against the ground. Later while the rest of the X-Men are still defeated from the Hulk's attack, Mercury tries one more time to defeat the rampaging green goliath. During the course of the battle, the Hulk was shown the recent graveyards of all of the deceased mutants that died after M-Day. Mercury then describes in detail the deaths of Laurie Collins and Brian Cruz, causing the Hulk to understand his self-righteous tantrum is wrongly directed towards Xavier’s affiliation with the Illuminati. Seeing these graveyards reminds the Hulk of his recent fallen companions on Sakaar, and with that understanding, he leaves Xavier unharmed
Children of X-Men
Cessily still maintains her disapproval and distrust of Emma Frost after overhearing her conversation with X-23 during the "Mercury Falling" arc. She also feels that Emma has carelessly "lost" track of Wither and constantly reminds her of the fact that Kevin is no longer in the school or under her surveillance. Mercury has also been deeply affected by the events of Decimation, as depicted in the "Endangered Species" miniseries. She is distraught by the death of a teenage civilian mutant and is one of the students at the institute trying to determine the youngest mutant, as she believes that the youngest mutant always tends to be killed.
Mercury is one of the New X-Men led by Surge that launch a strike against the Purifiers to incapacitate them and rescue the mutant baby. After Hellion is critically wounded by Lady Deathstrike, Pixie panics and blindly teleports the entire team out of the Purifiers' base, spreading them out between Washington and New York. It does not appear that Cessily suffered any lasting injuries as a result. She helps to stabilize Hellion in the X-Jet on the way back to the mansion. Later, she goes with Dust and Rockslide to visit the graveyard, and they discover that Predator X has entered the mansion grounds. Mercury battles the monster with the rest of the students and is transported by Pixie, along with the other New X-Men, to the battle between the X-Teams and Sinister's forces on Muir Isle.
Mercury and Rockslide are watching a training session between Pixie and Nightcrawler when Pixie stabs Kurt with her soul dagger. They run in and move Pixie away from Kurt's unconscious body, Beast enters and Pixie regains her senses. When she removes her dagger, Magik's soulsword emerges from his chest and Magik teleports in ready to reclaim her sword. Mercury engages Magik in combat and manages to stab her in the shoulder; Illyana responds by blowing her up, noting that she has some immunity to magic, but is not invulnerable. After Mercury reforms, she is placed on a team of X-Men being sent to Limbo along with Rockslide, all of them chosen due to their resistance to magic. Upon entering Limbo, the team fights their way through many demons. Pixie senses the darkness within her suddenly growing and she teleports off to Belasco's castle by herself. Hearing the screams from the castle, Kurt teleports the X-Men into the throne room. Once there, Witchfire turns Colossus and Wolverine against Mercury and Rockslide who get taken out, leaving Kurt the last X-Man standing.
Mercury, along with fellow students Onyxx and Loa, was tasked with keeping peace at the riots on Telegraph Hill after the mutant-hate group "Humanity Now!" marched from Sacramento to San Francisco to promote "Proposition X", displeasing many citizens of San Francisco, mutant and non-mutant alike. After the riots subsided on Telegraph Hill, Cyclops came and picked them up, taking them to City Hall. During the final battle against Norman Osborn's forces, along with Iceman and many of the other X-students, she takes on Mimic. After Osborn's defeat by the X-Men and the official creation of Utopia, Mercury is involved in a media tug of war between Norman Osborn, her biological father and their claims that she is being held captive against her will. Although she confronts her father over the phone, during a live television broadcast, and disputes his claims going as far as to call him a bad father before her situation gets more complicated as Deadpool intervenes. Believing that he is doing them a favor he attempts to kill Mr. Kincaid on live television only to be stopped by Domino. However Deadpool is still attempting to follow through and kill Mercury's father. In the mean time the X-Men plan on having Mercury declared an emancipated minor in order to counter Osborn.
Like all the X-Men, Mercury was trapped on Utopia. During the build up to Bastion's grand plan, she was seen as a bystander in the mess hall during Hope Summers' & Dani Moonstar's fight. Like all healthy & able-bodied X-Men, Mercury was sent to fight the hoards of Nimrods as they come flooding into San Francisco from a post-apocalyptic future. The first wave of Nimrod caught the mutants by surprise. Although Mercury wasn't hurt, she comforted Surge, who was left distraught after the first battle on the Golden Gate Bridge. At first, Mercury patiently waited alongside Loa & Gentle. They remained in the medical bay, watching over Hellion's unconscious body. While watching over her friend, she was surprised to see Trance return to her physical body. Trance was alarmed as she had come under attack while in Limbo on yet another mission to rescue Magik. However, Mercury had to break the terrible news that they couldn't help as they were under attack from the Nimrods.
Powers and Abilities
Liquid formation: composed of a non-toxic liquid mercury. Her form allows her to alter her shape in liquid form, extending blades from her skin or molding herself into different forms. Her ability to shapeshift extends to the most basic of rudimentary weapons. Her liquid mercury form is non-organic.
- Self-Sustenance: She is no longer a carbon-based life form and does not eat or breathe the same way as normal humans. Still, she consumes food out of habit and has not realized the scope of her change.
- Molecular Adhesion: Her liquid mercury form gives her the ability to cling to solid surfaces and move her body at will, even without overt locomotive features.
- Enhanced Durability: Her skin, bone and muscles transformed into liquid mercury to make it stronger and harder than human; impervious to injury to a certain extent.
- Magical Resistance: She is very hard to magically detect, attack or influence due to her non-organic form.
Electricity: As she most vulnerable in her liquid form, it is her main weakness and has often been used against her, because it causes her body to go haywire.
- The use of her powers can sometimes be embarrassing for Cessily: with her ability to re-shape any part of her body, she is able to "melt" herself and turn into a living puddle of mercury. When she does this, however, she is unable to keep her clothes on. Therefore, when she shapes herself back into her humanoid form, she will be nude.
- Her creators state that she is Irish-American.
- It has also been said by her creators that she can potentially do anything the T-1000 (Terminator 2) can.
- Cessily's is disappointed about not losing her powers due to M-Day.
- In her first appearance, she was sixteen-years-old.
- Mercury was also the name of one of the characters (a speedster) seen in Red Raven Comics (published by Timely Comics, the precursor to Marvel Comics). Various retcons have made it so that Mercury was the Eternal Makkari all along.
- A previous male character with the same name and powers was introduced as a part of Cerebro's X-Men.