Dark Super Sonic
From Sonic Retro
"Dark Super Sonic" is the fanmade name of the form that Sonic the Hedgehog takes in episode 67 of Sonic X. "Dark Super Sonic" looks exactly like Super Sonic, except he's completely black, has a blue aura, and no pupils.
Sonic achieved this form by accidentally channeling the power of the Metarex's fake Chaos Emeralds via his own anger. As such, "Dark Super Sonic" is completely rage driven. He quickly destroys both of the machines the Metarex were using to test Sonic and enjoys doing so (hinted by a mad cackle). Sonic powers down when he is calmed by Dr. Eggman who says Sonic normally acts much better than this. As the emeralds are later destroyed, "Dark Super Sonic" is never seen again.
Fans speculate that the form could appear in the games if Sonic channels the negative energy of the Chaos Emeralds. The events leading to Sonic's transformation into "Dark Super Sonic" are paralleled in Sonic and the Secret Rings, resulting in Sonic becoming the extremely similar Darkspine Sonic.