Super Sonic

This transformation can occur when Sonic is in possession of all 7 chaos emeralds, and at least 50 rings to balance and maintain the power. During this time Sonic is nearly unstoppable as he can fly at incredible speeds and the energy that is released can burst through steel doors or anything that is in his path.

Hyper Sonic

This form is very rare, and has only been seen once in the games. This form is activated by Sonic having the Super Emeralds in his possession. It is not yet clear how exactly the Super Emeralds are formed but they appear to be upgraded Chaos Emeralds. There is a theory that the Super Emeralds are created by the Chaos Emeralds spending a good amount of time with the Master Emerald and possibly being activated through Tikal's prayer.

Darkspine Sonic

This form is another very rare form that has only appeared once. Sonic was transported into another dimension to the world of the Arabian Nights where a being known as the Erazor Djinn was trying to collect the World Rings to rewrite history. In the final battle after Erazor Djinn absorbes the energy from some of the World Rings and becomes Alf-Layla-Wa-Layla. The left over energy was then channeled into Sonic from three of the rings, particually the World Rings of Rage, Hatred, and Sadness. Because of this while in this form his personality became more sinister and violent.