Metamorphia

Metamorphia is a female 'shape shifter', able to both transform herself into anything she wanted and change parts of her body independently of the rest of it, such as turning her hand into an anvil or blade. Metamorphia was an 'artificial life form' created by Grimer on behalf of Dr. Robotnik, whom she both idolised and loved (her room in his Death Egg had self-drawn pictures of Robotnik on the wall). She was desperate to please him and have her feelings reciprocated. She failed every attempt to destroy Sonic the Hedgehog and his Freedom Fighters, and when not in battle appeared to be very insecure and self-conscious.

History
Sonic first met Metamorphia when she, posing as a sweet bear, lured him into a trap in the Grim Zone, where Sonic thought she had perished after falling into one of the Zone's fiery pits, she in fact assumed a fire proof form and survived. Metamorphia returned in the guise of a rival green hedgehog named Cosmic, who challenged Sonic to a race to the end of the Emerald Hill Zone. "Cosmic" naturally couldn't keep up, but this had all been a ploy to lure Sonic away from his friends so that an army of badniks could attack them. Sonic escaped from Metamorphia and ran back to his friends. She tried to assume Sonic's own form to catch him, only to be attacked by the badniks and defeated again. She would resurface pretending to be Sonic's long-lost twin Tonic, though her cover was quickly blown and she was easily defeated by the Freedom Fighters.

Metamorphia fell from grace when she was assigned to destroy Shortfuse the Cybernik. Although she succeeded in defeating Shortfuse and capturing Tekno the Canary (Robotnik's former weapons designer) she failed to stop them detonating a large part of the Chemical Plant Zone. As punishment, Robotnik removed her shape-shifting powers and had her turned into a Badnik.

Some time later, Tails was attacked in the Grim Zone by the Badnik Metamorphia, who angrily blamed Tails and the other Freedom Fighters for making her like this. Once the Badnik shell was destroyed and Metamorphia was free, sobbing that she had failed again, she turned her back on being evil and said that she now hated Robotnik. Suddenly Metamorphia then experienced one last final change into a sweet bear (not much different from the form she took in her first appearance) and left to live a new life.

When Robotnik absorbed the energy of the Chaos Emeralds and attained godlike powers, Metamorphia was one of the enemies that Robotnik resurrected to battle Sonic. She was defeated when Sonic knocked Commander Brutus into Plasma, causing a chain reaction.

Trivia
Metamorphiamade a brief cameo in Archie Comics' issue #134 in a group of Robians as Sonic explains about the mass-deroboticization by the Bem.