Cosmo is an alien like plant who exists in the Sonic Anime only universe. Despite this, she is quite popular and is notable for having a relationship with Tails.
She is voiced by Amy Birnbaum
Slade Strikes Back
Cosmo also appeared in this story as an ally to M.O.D.A.B, and The Anime Empire against Slade and the Joker. She eventually joined with Boomer and his crew. At some point he and Cosmo were kidnapped by Slade and gave Boomer, his friends, Dib and M.O.D.A.B a phone call for them to stand down from Slade's plan or as he puts it "Your chocolate's been in my peanut butter for far too long". Dib, Boomer and the others go off to save Tails and Cosmo, After Slade puts them in a location, Bender confronts Slade about this as he told Slade not to harm M.O.D.A.B. Slade tells Bender that it was a loophole and that as long as he has them, Dib won't chase down him down or Bender by default even though they are the only ones who know of the allegiance. Angry, Bender demands Slade to tell him where they are. Slade tells Bender that they need to find purgatory as this is getting in their way, Before he shoots Slade, he gets a call from one of Boomer's friends. Tails is saved by the heroes and he continues to help him.
Legends of the Multi-Universe (Menslady's story)
Cosmo had been murdered by Daleks. When the Master told Tails of this, Tails let his desire for Cosmo get the better of him and became Dark Tails.
Later, Cosmo was revived on Cybertron with use of the Dragonballs. She was able to bring Tails to his senses and stayed with the Angels' team for the rest of the story.
LOTM: The Angels Return
When Angewomon and Myotismon sent out an S.O.S. for help retrieving Optimus Prime's memories, Tails was one of those who got the message. Cosmo insisted on accompanying him and Tails agreed, but he did some insisting of his own: that Cosmo stay near him.