Auto-Fiona (referred to only as "Fiona Fox" or "the Auto Automaton") was an Auto Automaton built by Dr. Ivo Robotnik based on a young Mobian vixen named Fiona Fox, who was being held as a prisoner by him in a mine at the time, but Auto-Fiona was not activated immediately.
Many years later, Doctor Robotnik saw an opportunity to use the robot when one of his secret cameras, hidden in a tree near Knothole's dock, saw Tails storm off in his Sea Fox after being attacked by an amnesiac Sonic. Intending to roboticize Tails, Robotnik laid a trap on an uncharted island and activated Auto-Fiona to serve as bait. As Tails passed the island, he found Auto-Fiona tied to a tree and screaming for help. Flying out of the submarine, Tails was immediately smitten and untied her. Believing her to be a real vixen named Fiona Fox, Tails spent a romantic day with her, until she lured him to a hidden roboticizer in her den.
Tails managed to escape, shedding fur from his twin tails by twirling them, thereby clogging the machine's combines and causing it to explode. Fiona then let loose an all out attack on Tails, punching him, swinging at him with a club, and even trying to drown him. However, while holding him down, the water leaked into her metallic body and made her rust, permanently paralyzing her. Tails then took Fiona out of the water and placed her on the island as a monument to his "lost youth". While cleaning up the litter Robotnik had left behind, Tails found a list of supplies that confirmed that Robotnik had plans for a satellite operation elsewhere on the planet. Believing that the Freedom Fighters would leave him behind if he called Princess Sally, he decided to going on this mission alone. He said his final goodbyes to the immobile Fiona, who could only watch as he pulled away in the Sea Fox.
As he left, she shed what appeared to be a single tear from her eye.
Auto-Fiona was skilled at manipulation judging by how easily she had Tails fall in love with her, and she also had super strength and could use melee weapons such as clubs. Her only known and major weakness was the fact that she wasn't waterproof and rusted very easily after a short period of time. Although, she was still able to drink liquids and not become rusted. It's also possible that she can experience feelings, as shown when Tails left the island, she let out a tear, indicating that she may love him.
Like the real Fiona Fox, she had dark red fur and blue eyes.