BIOGRAPHY
Not much is known about the history of the woman named Siena Blaze. She was apparently raised in the American southwest and had a relationship with her father, but nothing else is known about her family background. One reference was made to her being a "woman of privilege," although whether that referred to her class status or genetic pedigree is unknown. She is also apparently hydrophobic, freezing up when washed away in a river, unable to swim or defend herself. Siena believes she was never loved by anybody in her life, which hardened her feelings towards humanity long before she discovered she was a mutant.
Siena Blaze's mutant power would be dangerous even in the most responsible hands. Like her father told her when her powers first manifested, Siena's ability to disrupt Earth's electromagnetic field risked destroying the entire ecosystem every time she used it. While Magneto could be compared to a master sculptor, bending and shaping electromagnetic waves to flow in the direction he wanted, Siena Blaze's power was more akin to ripping out a chunk of Earth's electromagnetic field and throwing it in someone's face. The damage she caused to Earth's E.M. field, even as a side effect of her main power displays, could potentially have permanently negative consequences to the environment. [Stryfe's Strike File #1, X-Men Unlimited (1st series) #1]
Siena Blaze did not care. Although she reportedly only used her powers once more after she and her father witnessed her original manifestation, it wasn't out of care or empathy for the planet -- she simply didn't know how to control it. Wanting to establish herself as a criminal and an anarchist, Siena recruited a partner named Wallace Benton with her assets and the promise of being a super-powerful mutant. Unfortunately, whatever their crime spree entailed, it soon led to the duo being trapped behind their own crashed car on a deserted stretch of US-1 in New Mexico with the authorities shooting to kill. Wallace pressured Siena to use her mutant powers to save them, but Siena was still too scared to use her powers for fear of hurting herself.
The decision was taken out of her hands when Trevor Fitzroy and Bantam arrived through one of the former's time portals. Fitzroy callously drained Wallace of his life energy to recharge his own powers, something Siena shrugged off with little concern. With a new time portal, Fitzroy summoned a massive armored prisoner transport from his own timeline, guiding its speeding trajectory through his portals to crash through the highway patrol and pass back through to its own time. Siena Blaze briefly caught a glimpse of her own face among the prisoners, several decades older.
Fitzroy revealed that he knew Siena Blaze from his future and offered her a position in the Upstarts on behalf of their arbiter, Gamesmaster. The Upstarts were a group of mostly mutants competing with each other to kill the most mutants in a sick "king of the hill" competition. The prize at the end of the contest was often vague: some accounts were the winner would receive the assets and resources of all the other players, other reports indicated the winner would actually gain the mutant powers of the losers, or even immortality or omnipotence itself. Regardless, Siena Blaze was willing to play -- her complete lack of regard for human life meant she had no qualms whatsoever about killing others for her benefit, no matter what the ultimate prize ended up being. [Uncanny X-Men Annual #17]
Siena Blaze chose to shoot big for her first hunt on the Upstarts, targeting the X-Men's leaders Cyclops, Storm and Charles Xavier. Supplied with a support staff by Gamesmaster, Siena set up an ambush in the cold wastes of Antarctica, tracking the X-Men's Blackbird as it made a visit to the Savage Land. When it left to return home, Siena unleashed her power to blow a massive hole through the jet, simultaneously causing a scar in the planet's electromagnetic field that created a freak blizzard and an impassable interference flux in the air, preventing any rescuers from reaching the crash site.
The trio miraculously survived the crash, although they were alone and without aid in the middle of Siena's blizzard. When Gamesmaster informed Siena her targets still lived, she killed her support 
staff and blew up their constructed base in a fit of rage. Using her remaining mini-ship, she tracked Storm's power signature and confronted the X-Men directly. Battered and bruised as they were, the X-Men were still a match for Siena Blaze, as Xavier psychically forced her to release her power while Storm and Cyclops funneled it away from them. Siena Blaze decided to cut her losses and teleported away, leaving behind an electromagnetic vacuum implosion as a last ditch effort to eliminate the X-Men. [X-Men Unlimited (1st series) #1]
She still failed but, at her first official meeting with the Upstarts, the Gamesmaster awarded her some points in the competition for the mere chutzpah of thinking big on her first "kill." [Uncanny X-Men (1st series) #301]
Gamesmaster occasionally allowed other "sponsors" to intervene on the Upstarts competition to 
make the game more interesting. When Mister Sinister came to him, Gamesmaster agreed to craft a mission for Siena Blaze on his behalf. Siena was sent to Muir Island to retrieve a digital map of Proteus' genetic sequence, giving Sinister access to one of the most powerful mutants who ever existed. Gamesmaster declared Proteus' mother Moira MacTaggert redundant, meaning Siena had the opportunity for extra kill points on this job.
Siena's powers caused an explosion at an offshore oil rig near Muir Island as a distraction while she approached the island. Expecting a quick kill, Siena Blaze was unprepared for the mutant team Excalibur, who had recently taken up residence on Muir. Still, she sensed Nightcrawler's arrival due to his teleport signature fluctuating the magnetic fields as he passed. By playing with those fields, Siena forced him to materialize inside solid rock. Shadowcat barely managed to phase them free before their bodies were ripped apart from within.
Moira, Siena Blaze and Excalibur engaged in a game of cat-and-mouse through Muir until Phoenix returned from the rig as well. Rachel Summers had been hard at work using the Phoenix Force to 
repair the damage done to the atmosphere and magnetic field of the planet by Siena's "distraction." Phoenix turned some of Siena Blaze's power back against her, forcing the women to fight hand-to-hand as Siena scratched Rachel across the face. Seeing victory slipping from her grasp, Siena decided to teleport away instead of risking further combat (although Phoenix contained her electromagnetic backwash, so even her departure didn't harm Excalibur any further). Mister Sinister was greatly displeased with Gamesmaster and Siena's failure, but he changed his mind when he learned Siena had a sample of Rachel Summers' DNA under her fingernails. This sample for his collection led Sinister to leave the Upstarts without any malice. [Excalibur (1st series) #72-74]
The Upstarts competition neared a conclusion as Gamesmaster took a stronger role in the day-to-day activities of the contest. His next game was a "Younghunt," targeting former members of the New Mutants and Hellions for capture, only to later kill them for the necessary "points" when the hunt concluded. Siena Blaze kicked off the Younghunt by capturing Cannonball and Boomer of X-Force. She bit off more than she could chew on her next strike, however, confronting Moonstar, Empath and Karma, the last of whom seized control of Siena's mind. Karma had Siena deliver them to the Gamesmaster in order to infiltrate the Upstarts' base in Switzerland.
Gamesmaster was an omnipath, however, and aware of Karma's ploy. He took control of Siena himself, turning Karma's puppet against her. With X-Force and the New Warriors in Switzerland to rescue their captive friends, Gamesmaster manipulated Siena Blaze as a pawn along with the various other captives against their rescuers. Paige Guthrie challenged Gamesmaster to a new game of preparing the young mutants of the next generation for the future, leading him to abandon Siena and his other puppets to chase this new venture. As Shinobi Shaw and Graydon Creed cut their losses, and with Fenris, Fabian Cortez and Trevor Fitzroy all presumed dead or out of action, the Upstarts and their competition were finished. [X-Force (1st series) #32-33; New Warriors (1st series) #45-46]
At loose ends without Gamesmaster, Siena Blaze had no goals or purpose to drive her forward. She apparently attempted to keep the Upstarts competition going on her own, not because there 
was still a prize to compete for, but because she simply had nothing else to fill the emptiness of her life. After being contacted by Reaper for potential membership in the Mutant Liberation Front, Siena Blaze responded to his query just to kill him and claim "points" for the Upstarts competition. Siena had acquired energy-conduit handguns as a means of channeling her all-destructive power into more controllable discharges. When Reaper damaged her guns, however, Siena unleashed her full energies in a massive eruption of electromagnetic force.
In the aftermath of Black September, the Marvelverse and Ultraverse were still tied together in the dimensional fabric. At the same time as Siena Blaze unleashed her power, the similarly devastating power of Amber Hunt exploded from within her in the Ultraverse. This somehow created a link between the two women across the dimensional void, drawing them up into extra-dimensional space. After being buffeted about in a reality vortex of unprecedented strength, Siena Blaze and Reaper crashed down onto the Godwheel with Amber Hunt, the Ultras Shuriken and 'Strike who had been hunting her, and Juggernaut, whose exile in the Crimson Cosmos was also 
caught up in the reality storm. These "Exiles" banded together to survive the harsh conditions of the Godwheel and the strange creatures they encountered on the way. Reaper was secretly met by a Tradesman who provided him with dimension-crossing technology in his scythe. Returning to the group, Reaper used his scythe on Siena and Amber, recreating the link between the two women and completing the crossing begun by their power eruptions, sending the six Exiles back to Earth. [All New Exiles Infinity]
Well, AN Earth. The Exiles materialized near Central Park in the New York City of the Ultraverse. Their arrival coincided with a wave of destruction sweeping across the city, killing millions with it. The Exiles were blamed for the devastation known as "Ground Zero," and a million dollar bounty was placed on each of their heads. Unable to prove their innocence (even uncertain of it, to be honest), the unlikely companions remained together for mutual protection. Siena Blaze, Juggernaut and Reaper soon came to recognize that this Earth was not the same as their home. Major landmarks like Four Freedoms Plaza were missing from Manhattan, and they also found their powers dramatically lessened by the physical laws of the Ultraverse versus their own reality. In Siena's case, this was almost a blessing, as her powers no longer threatened the stability of the planet every time she used them. [All New Exiles #1]
The X-Men soon came looking for Juggernaut and the other missing Exiles, crossing dimensions thanks to their ally Gateway, and starting a brawl between the two groups. When Reaper tried to force Gateway to send him back home, the Exiles discovered the process was more complicated than they thought. An entity known as the Firewalker now existed in extra-dimensional space, linked to the Exiles and able to feed off of their life energy as they passed between dimensions. Unable to return home without unleashing the Firewalker and possibly dying themselves, the Exiles were trapped in the Ultraverse. Seeing no way to force the villains home, the X-Men departed via Gateway without further conflict with Blaze and the others. [Exiles vs. the X-Men #0]
Siena and the Exiles were on the run and forced to move around frequently, using the money and resources of their self-appointed leader 'Strike as necessary. Siena was turned on by 'Strike (Brandon) and tried to seduce him early in the team's existence, but Brandon was repulsed by Siena's amoral personality and focused on trying to prove the Exiles weren't responsible for 
Ground Zero. Still, he did seem to be warming towards Siena in later months as the team went on a skiing vacation, and she remained protective about him. [All New Exiles #2, 5, 7] When 'Strike had a precognitive vision that inter-personal relationships on the team would destroy the Exiles, though, he made an edict banning such coupling. His vision actually pertained to potential new members Buck Lonestar and Velvet Fist, who were sent by the government agency Aladdin to break the team up. Sure enough, Siena Blaze and Amber Hunt briefly fought over Lonestar, thanks to his ultra-enhanced charisma, but the seductive siblings were soon found out and driven off. [All New Exiles #9-10]
The Exiles returned to Ground Zero in an attempt to gather evidence and clear their names. However, they were confronted by a slew of bounty hunters and the alien entity known as Maxis who decimated the team. [All New Exiles #11] In the second round of their battle, the Exiles were joined by UltraForce, but only barely managed to fight Maxis to a stalemate. [UltraForce (2nd series) #12] Things escalated even further when an alien invasion force arrived on Earth seeking the Demonseed, the true author of Ground Zero's devastation. The Exiles, UltraForce and Maxis joined forces in opposition to the Alien Elite. In the aftermath, the Exiles and UltraForce learned 
Maxis had the ability to cross dimensional barriers (and apparently side-step the Firewalker problem). Black Knight of the Avengers decided to leave UltraForce and return to his home Earth, and so Reaper and Siena Blaze joined him, leaving the Exiles and Ultra-Earth behind. [Ultraverse Unlimited #2]
Siena Blaze laid low for some time after returning to her home Earth, but eventually became a target for the new Weapon X Program. A secret black ops organization operating with at least tacit approval from elements in the government, Weapon X began quietly rounding up mutants in America and carting them off to a concentration camp called Neverland. Reaper and Siena Blaze were among the prisoners whose powers were constantly dampened inside the campgrounds. The mutants were broken down into two categories, with Siena's group including those who were useless to the program or potentially too powerful to contain. Siena Blaze and a few dozen of her fellow prisoners were herded into a small room and then murdered en masse. [Weapon X (2nd series) #5]
Since that time, Siena Blaze resurfaced as one of a number of dead mutants reanimated by agents of Selene using the techno-organic virus. Virtually indestructible and enslaved to Selene's will, Siena and the others attacked the X-Men on their island base of Utopia. [X-Force (3rd 
series) #22] When Selene was confronted by X-Force on Genosha, her servant Blink tried to recall all the mutants from Utopia as reinforcements. Those that returned died again when Selene was cut down. However, it was reported that some of the reanimated mutants survived and escaped without being returned to their graves. Apparently, Siena Blaze and her fellow Upstarts, Shinobi Shaw and Fabian Cortez, were among these escaping mutants. [X-Force (3rd series) #25]
Time passed and mutantkind reached some of its darkest days. The X-Men were nearly all wiped out in a major battle and a cure for the X-Gene was being distributed amongst the public. Siena, Cortez, Shinobi and a returning Trevor Fitzroy reunited as the Upstarts. Their intent was to go out on their own terms, spending these final days killing the remaining mutants until only they were left. The Upstarts murdered the Nasty Boys and used them as bait to lure out Cyclops and his dwindling, few remaining X-Men. Despite setting their trap, the Upstarts had no strategy or plan for defeating the X-Men. The coordinated teamwork and tactics of the X-Men brought down the Upstarts, with Cyclops assisting Magik against Siena Blaze. [Uncanny X-Men (5th series) #20]
The Upstarts were imprisoned in the makeshift holding cells beneath Harry's Hideaway where the X-Men were stationed. The aggressive anti-mutant agency the Office of National Emergency began making moves against the X-Men, who united with the Hellfire Club. Emma Frost had a plan of action and sent several X-Men to retrieve Fabian Cortez from Harry's. They succeeded, but it was reported that Fitzroy and Siena Blaze may have been killed by O*N*E forces that caught them there. [Uncanny X-Men (5th series) #21]