Throughout the Sonic the Hedgehog series, Sonic can transform into various super powered forms of himself, surrounding himself in an aura of power of a certain color and gaining other powers such as flight, increased speed and strength, energy manipulation, and invincibility.

Here is a list of some of his forms:

Dark Super Sonic

"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 eyes.

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 do (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

 Darkspine Sonic

In this form, Sonic has increased strength and the ability to fly, along with his ring powers Time Break and Speed Break. His attacks are also more close-combat based, as opposed to the boosting and energy moves that Super Sonic uses.

His fur becomes bluepurple in color with two golden rings around his wrists and two around his ankles. His gloves and shoes disappear, too. Two white lines come down from the middle of his forehead and white markings outline where the straps of his shoes were. His skin turns pale white, and his irises, pupils and mouth disappear. Also, his voice has a slight change, becoming more demonic, but maintaining Sonic's pitch, possibly due to the negative ring energies that give a slightly evil side effect.

Sonic the Werehog

Arguably one of the least coolest forms of Sonic, he transforms into a bestial wolf-like form. When transforming into the Werehog (or transforming back to normal), a light and a cloud of purple smoke envelops him. Sonic appears to retain most of his normal abilities in this form as well as the ability to speak, though with more of a growl than normal.

Super Sonic

As Super Sonic, Sonic is faster and stronger, and he is gold in color and aura.

Hyper Sonic

Hyper Sonic has all the benefits of Super Sonic, such as invincibility, improved speed, and greater jumping abilities, but Hyper Sonic also has some improved abilities such as the ability to breathe underwater, further increased speed, power, and a double jump attack that will destroy all enemies within the direct vicinity, excluding bosses

Excalibur Sonic

He dons shining gold armor covering his entire body and carries Excalibur in his right hand. A red cape runs down the back of his armor.  Watch the video for sonic's transformation.