She was voiced by Ashley Tisdale.
In "The Last Donnycorn", Tanya and the other three members of The Four Unicorns of The Apocalypse went to jail for doing evil. Their prison cell was the dark magic dark mirror of darkness. They were eventually set free, by Donny, making a silly face into the mirror. After her freedom from jail, she and other other unicorns banded together once again, to take over all of Unicorn World.
The team's first order of business was to attack Unicorn World and build an evil empire, where team leader, Stanicorn would sit atop a giant throne and absorb all the powers of the other unicorns in Unicorn World and utilize them to destroy Unicorn World. Meanwhile, Tanyacorn and the other pawns would stand guard of his throne. Tanyacorn just goofed off the whole time, annoying Stanicorn.
Tanyacorn fought with Bubbles, merely having a childish pillow fight. The two played their pillow fighting game for a while, laughing and having fun, but not actually causing any real damage to each other.
After the demise of her team leader, Stanicorn, Tanyacorn redeemed herself and stopped being evil. She made her new leader Gretel, and became a nice, functioning member of the society of Unicorn World, alongside her now good-hearted teammates, Joeycorn and Petercorn.