Medusa in Mars' colliseum.
Medusa was a cyborg with a mar'kak as its organic component and was one of the three "legends" used by ex-System Lord Mars in his Colliseum on the graveyard planet Kar'tek. It, along with the other legends, had never been defeated in combat until the planet was discovered by SG-1.
When Mars sent Teal'c into the colliseum to face against the legends, he first faced off against the Minotaur but managed to defeat it with an energy sword before Medusa was able to attack him. Medusa's attacks involved the use of the robotic snakes which sat on her head, using them to try to bite Teal'c. Teal'c managed to grab ahold of one of these, however, and severed it from the main body before slicing across Medusa's neck and killing the cyborg. (SG1: "Fall of Rome 2", "Fall of Rome 3")