X-Men (2nd series) #171
X-Men student body,
• Mutated physiology provides him
with four eyes, a hinged jaw, and
an organic rock composition
with superhuman strength,
endurance, and resistance to physical injury
Sidney Green was born to parents who, for reasons of their own, felt that they were unable to look after him. Placed in the New Jersey social services care system, Sidney was bounced between foster families, making him feel like a social outcast. This insecurity was compounded by his clumsy and awkward attitude, all of which combined to make him an easy target for bullies. When the stress of it all caused him to become a chronic bed wetter, Sidney was driven to the point where he would dehydrate himself to try to stop it.
For most children, having their body turn to living rock would be a horrifying experience. However, for a troubled teen like Sidney, when his mutation manifested it was a blessing. Now literally unable to wet the bed, Sidney was finally able to sleep through the night. Due to his obvious mutation, the social care system was unable to deal with him and Sidney was enrolled in the Xavier Institute, finally giving him a permanent home with others just like him. [X-Men: The 198 Files]
At the time, the large class of students at the Institute was broken up into training squads and Sidney was put onto the Chevaliers, led by veteran X-Man Gambit. Taking the name Onyxx, Sidney bonded with the rest of his squad, among them Bling!, Rain Boy and Flubber, all of whom had obvious physical mutations like him. One day a new student named Foxx arrived at the Institute and Onyxx was immediately infatuated with her. She was placed on the Chevaliers squad, much to his delight, and Sidney wasted no time in trying to chat her up. Foxx was not interested one bit, as she had eyes for Gambit, and she abruptly dismissed Sidney’s advances.
Unfortunately, Onyxx was so obsessed with her that he was unable to see she was uninterested. Due to this, he believed that Gambit was the one chasing Foxx, and one night he confronted his mentor directly. Attacking Gambit, Onyxx demanded that Foxx be left alone, only to be soundly beaten by the more experienced X-Man. The rest of the Chevaliers arrived to break them up and all of them sided with Onyxx, who was looking a little worse for wear.
When it was revealed that Foxx was actually just a faux persona of the shape-shifting Mystique, the X-Men and the students were all shocked. Onyxx was in a state of disbelief over it all and even attacked Flubber when his teammate taunted him over it all. Angry and betrayed, he confronted Mystique, who was being held in the X-Men’s brig until the situation could be resolved. Believing that she had been flirting with him the whole time, Onyxx couldn’t handle the truth and flew into a blind rage, attacking Mystique. Proving that sheer strength was no match for wits, she soundly beat him by smashing him around the head with a toilet bowl. Afterwards, Onyxx was hospitalized whilst Mystique slipped out of the Institute, putting an end to the whole embarrassing situation. [X-Men (2nd series) #171-174]
Sidney was one of the few mutants to keep their powers after M-Day, whilst many of his fellow students, Flubber and Rain Boy included, lost theirs. The various training squads were dissolved and the students were forced to fight each other to earn a place on the one-and-only remaining squad. Onyxx wasn’t selected as part of the team, but was nevertheless still drawn into a number of deadly situations. One such occasion was when the numerous anti-mutant groups all descended on the Institute looking to wipe the remaining mutants out. [X-Men: The 198 Files, New X-Men (2nd series) #23]
When the X-Men moved to San Francisco, Onyxx joined them and set about making a home for himself there. When the ballot initiative limiting reproduction rights of mutants called Proposition X was proposed, riots erupted throughout the city and Onyxx worked alongside the other X-Men to help keep the peace. At the end of the crisis, the X-Men constructed an artificial island off of the coast of San Francisco and declared it a sovereign nation, separate and independent from the United States. Onyxx joined the rest of the X-Men when they moved to this island they called “Utopia.” [Utopia Crossover]
It was hoped that the island would be a safe home for the world’s mutants, but it soon turned out to be the opposite. Utopia had to weather numerous attacks, one of which being from the vampiric mutant Selene and her undead army. Selene had surrounded herself with powerful mutants and with them invaded the island in the hopes of finding a special ceremonial dagger she needed. One of her Inner Circle was Wither, a former friend of Onyxx’s who had the power to disintegrate living tissue. Whilst Wither was distracted fighting Dust, Onyxx tried to sneak up on him, hoping to knock him out. Tragically, Wither was quicker and he used his deadly power on Sidney, disintegrating his stone body within a matter of seconds. Although Selene was ultimately defeated, Wither and the Inner Circle escaped, leaving the X-Men to count their losses and mourn Onyxx. [Necrosha crossover]