At some point, the Chaos Council, which is an evil group of science and technology geniuses related to Dr. Robotnik, turned Rusty Rose into a cyborg and brainwashed her into obeying them, making her their top enforcer.  Her entire body except for her head is robotic, making her a cyborg.  Rusty possesses Amy's common sense, desire for efficiency, and fighting ability, but stripped of any compassion to others.  She contains a pink Flicky within her chest cavity, which is used to power her.