This transformation exists primarily within the Sonic X continuity.
Information in this article may not be canonical to the storyline of the games or any other Sonic continuity.
Cosmo's transformation is a transformation used by Cosmo in the anime series Sonic X.
Earthia appeared to her and told her only she could save the universe. Cosmo's amulet then shattered and she transformed, helping Super Sonic and Super Shadow defeat Final Mova, an enhanced form of Dark Oak. Eventually, she sacrificed herself and fused with the Dark Oak planet, allowing Miles "Tails" Prower to fire the Sonic Power Cannon, destroying the planet and killing Dark Oak and Cosmo. In the Japanese version, Sonic and Shadow used Chaos Regeneration in order to keep her alive. However, it turned her into a seed no one can react with. In the dub, Chaos Regeneration is not used and Cosmo implies the seed is her child.