Nega Cyborg is an evil clone of Cyborg created by Trigon.
History
Since Cyborg, Starfire and Beast Boy are protected to Trigon's powers thanks to the Ring of Azar, he refuses to expend more of his energy to destroy them and uses his powers to create evil clones out of each of them and pits them against each other, each against his or her own clone.
Nega Cyborg has knowledge of Cyborg's weak points and uses them to full advantage during their battle. He also taunts Cyborg with the death of his mother.
Later, as the tide of the battle above ground starts to turn against the Teen Titans, they decide to switch combatants in hopes of regaining the advantage. Therefore, Starfire fights against Nega Cyborg and manages to beat him.