Mecha Sally is the roboticized version of Sally Acorn. Sally assumed this guise two times: once in a failed attempt to sabotage Dr. Robotnik, and the second in a moment of sacrifice during a battle against Dr. Eggman.
Becoming the Enemy
Bunnie had the idea of allowing one of them to be roboticized so they could sabotage Robotnik's headquarters right under his nose, and then be reverted back to normal later. Sally herself volunteered to be roboticized. Days, later, when Sally (equipped with a Neuro-Overrider) purposefully allowed herself to be captured, it was carried out. Unfortunately, the device fell off of her, and Sally was completely subjected to the roboticization sequence, losing her free will just like all the other Robians. Now dubbed "Robot Number Three-Three-Nine-Zero" by Robotnik, Sally revealed the secret exit to Robotropolis she was to meet the Freedom Fighters at, and captured them all with the exception of Sonic, who was busy keeping Robotnik's SWATbots occupied as a diversion. Upon returning, Sonic saw his friends captured and in the presence of Robotnik, Snively and the robot Sally. After the Freedom Fighters refused to tell them where the De-Roboticizer was, Robotnik ordered them all to be roboticized at the hands of Sally herself. Fortunately, Dulcy came in the nick of time with the De-Roboticizer, and turned Sally back to normal with it before she roboticized her own allies. (StH: #29)
After discovering Dr. Eggman's plan to roboticize the entire planet, Sally went to stop the roboticizer as Sonic fought Dr. Eggman and his Sonic robots. Sally crawled beneath a floor tile, crammed between large cables, and she hooked Nicole into the system again. Sally desperately looked for a way to block the roboticizer's command signal or otherwise prevent its firing, but with as little time as they had, Nicole informed her that it would be impossible, the only option available would be to invert the beam. Without hesitating, Sally ordered her to do so, setting up a manual executable before ensuring Nicole's core programs would be safe back in New Mobotropolis. Worried, Nicole protested, saying that Sally would not be immune. Sally told her friend that she'd been given a second chance and the opportunity to save everyone with it and she needed Nicole's help. Once Nicole had finished her download (leaving behind a message of good-bye as well as the executable), Sally held back her tears and steeled herself. Just as Eggman ordered the world roboticizer to fire, Sally smiled sadly, said good-bye and executed the program. The roboticizer fired, but to everyone's shock, it rebounded into the very chamber it was in, destroying much of the machinery (including the two robots) and causing a large explosion. Sonic and Eggman struggled from within the rubble, the hedgehog mocking the doctor for once again having a plan thwarted by the heroes. However, Sally suddenly emerged from the rubble, roboticized and damaged by the explosion. As Sonic looked on in horror and Eggman cackled in delight, Mecha Sally reached for Sonic, coldly saying, "Hedgehog. Priority one." (StH: #230)
Mecha Sally then seized Sonic by the throat, with Sonic pleading with her to fight Eggman's control, begging her not to make him fight her. Eggman, delighted about this turn of events, stated that while it would be sensible to order her to march the two of them into an incinerator, he wanted to enjoy this and had Mecha Sally throw Sonic out of a waste disposal hatch. She then accompanied Eggman (who commented about finding a better name for her than 'Mecha Sally') to the bridge of the Death Egg where they were met by Snively. When Snively objected to Eggman's order to launch an assault on New Mobotropolis, stating that the Death Egg was too heavily damaged, Eggman had Mecha Sally grab him by the collar of his uniform and demand that he follow her master's commands. (StH: #231)
Not long after, Eggman presented Mecha Sally to his assembled Grandmasters alongside other Metal Series robots as enforcers to "help" the Dark Egg Legion chapters perform effectively. Once the Grandmasters were dismissed, Mecha Sally accompanied Eggman aboard the Egg 'Stache Flyer in search of the fleeing Snively. Tracking Eggman's nephew to Central City Mecha Sally provided support for the Egg Paladins by confronting E-123 Omega. Sally's appearance in serving Eggman shocked even the E-100 Series robot into contemplating rescue, or possibly destroying her as an act of mercy. However, Mecha Sally and Metal Sonic v3.6 took Omega by surprise with their combined firepower. As Snively escaped again, Mecha Sally and Metal Sonic destroyed the G.U.N. fighters pursuing his Egg Jet and then withdrew to continue the chase.
While attacking Stormtop Village she engaged Monkey Khan, but the fight drained her Power Ring and threatened to kill her without a replacement. Khan selflessly gave up his Power Ring crown to save her, and upon being restored, subdued him so Eggman could take control. Both were crushed under some trees when Snively arrived with the Iron Oni, but Mecha Sally freed herself and faced Khan again after Regina possesed him with her Magitek. Khan overpowered Mecha Sally as they fought, and she fruitlessly attempted to use his feelings for her to an advantage. Regina's hold over Khan broke before he could finish her though, and Mecha Sally entered emergency stand-by whereupon Khan handed her back over to Dr. Eggman, as he was the only one who could repair her.
After being fixed, Mecha Sally was sent with Egg Swats to invade Furville and make an example out of the inhabitants. However, their troops were repelled when Team Fighters arrived on the scene and Sally had to retreat with the ground forces providing cover fire as the Death Egg headed south for the Lost Temple of Shazamazon. While Eggman refueled and restocked the Death Egg, Mecha Sally kidnapped Queen Hathor and Grand Chief Lupe Wolf in order to turn the Felidae and the Wolf Pack Nation against each other. The plan soon went awry though, when Hathor escaped and led Team Fighters back to the base. Mecha Sally discovered Tails with T-Pup near the Death Egg, and was surprised that his emotions no longer impaired him as they clashed. She then gave Tails the choice to try disabling her before the Death Egg departed, risking himself and the others, or let her go so they could escape and save the region. Tails decided it would be best to leave, and Mecha Sally returned to the Death Egg, unaware Tails placed a tracker on the fortress. After the airship took off, Mecha Sally offered a "divide and conquer" tactic, to which Eggman decided to have her divert Team Fighters by visiting Elias' family.
Mecha Sally then led the assault on Feral Forest as Team Fighters caught up to her and had a rebuilt Silver Sonic v3.0 take on Sonic while she bested Colonel Sommersby in his attempt to delay her. She was then blocked by Amy before she could proceed, and tried to infer Amy's actions as a way to get rid of Sally and have Sonic all to herself. Amy resisted her goading with Tails' help, forcing Sally to set fire to nearby houses with her Boom Fant as a distraction, and called for back-up from the Egg Swats aiding in the raid. While her old friends fended off the Egg Swats, she discovered Elias and his family already left, and she flew off from her failed mission to join the Death Egg's second invasion of New Mobotropolis.
Search and Rescue
Team Fighters's pursuit of the Death Egg lasted quite a while, with Eggman making several more attempts to keep the heroes stalled. Eventually, the Death Egg landed in the Northern Tundra, where Team Fighters, aided by the Arctic Freedom Fighters, launched an assault to rescue Mecha Sally at last. Silver the Hedgehog, who had come to the conclusion that the roboticized princess was in fact the mystery "traitor" to the Freedom Fighters that he had been searching for to save his doomed future, also arrived to assist Team Fighters in the rescue, having realized that her "betrayal" was not of her own free will.
Soon enough, Eggman, outraged that Sonic and his allies were right on his tail yet again, deployed Mecha Sally along with a horde of Egg SWATs to hold them off. While the Egg SWATs overwhelmed the Arctic Freedom Fighters, Mecha Sally went for Team Fighters, first by kicking Amy in the jaw. Sonic grabbed her and rammed her backwards against a bulkhead, only to be incapacitated along with his friends by a powerful blast from her head-laser. At that moment, it seemed like she had the team at her mercy, but just before she could finish them off, she was discretely knocked out by Silver, who basked in the fact that he had successfully stopped the "traitor". Just then, however, the world faded to white as it did before, much to Sonic's surprise...