From Sonic Retro
Darkspine Sonic is one of Sonic's super forms. Darkspine Sonic appears at the end of Sonic and the Secret Rings. When Sonic accidentally absorbs the power of the World Rings, he is transformed into an angrier version of himself similar to Dark Super Sonic from Sonic X.
Darkspine Sonic's quills point downwards and he turns a deep indigo color (which is much brighter in the CG scene). He loses his pupils, shoes, and mouth and his muzzle, chest, and ears turn white. He wears giant rings around his wrists and ankles and gains two stripes on the top of his head and the middle quill of his back. He is also surrounded by an aura of fire.
Darkspine Sonic is able to fly, but is not invincible and doesn't depend on rings. He can be attacked just like regular Sonic and can keep his form with no rings. Unlike Super Sonic, Darkspine Sonic takes a more physical approach to fighting as he attacks with barrages of punches and kicks as opposed to Super Sonic's head butting. Additionally, Darkspine Sonic has a much gruffer voice than normal, which resembles the voice of the Werehog. This transformation was brought on by the Sonic absorbing three of the seven World Rings, at the death of Shahra he took on the rings of sadness(purple), rage(red), and hate(green).