For those who aren't aware or haven't played the Sonic and the Secret Rings game, th Darkspine form is the new super form that Sonic assumes in the game after he absorbs the powers of the three negative rings (Sadness, Rage, and Hatred).
I thought to myself...well what happens if he were to absorb the four other rings(Prayer, Joy, Pleasure, and Wishes)?
Well my theories, added in with a little fan fiction Role Playing brought about this doodle. I sorta envisioned a figure like the goddess Isis, mixed with an angelic theme.

Stealth's body and color lighten, her quills appear more feather-like, the white Markings changed into something more tribal, the rings changed position, there is a ring Halo over her head, and the rings encircling her arms are emitting wings of fire, rather than having a flame coming from her breast.

Sonic the Hedgehog, Secret Rings, Darkspine © Team Sonic & Sega
Stealth "Stella" the Hedgehog © Me
Lightquill © Me, I guess. ^^;