Sonic the Hedgehog protagonist Sonic the Hedgehog, a blue hedgehog able to run at supersonic speeds, and recurring villain Dr. Eggman, an evil scientist whose ambition is to conquer the world. Among Sonic's many allies, the most well-known include: Miles "Tails" Prower, a twin-tailed, highly intelligent yellow fox who is Sonic's sidekick and best friend; Amy Rose, a pink hedgehog who is Sonic's self-proclaimed girlfriend and a hero in her own right; Knuckles the Echidna, a coolheaded red echidna who is the guardian of the Master Emerald; Shadow the Hedgehog, an anti-heroic doppelgänger of Sonic with a dark past; and Metal Sonic, a
Sonic the Hedgehog speed, near-invincibility and a change in color. In some games, characters are still vulnerable to being crushed, drowning, falling into a pit or running out of time. Depending on the type of transformation, the condition to attain such a form is an individual making contact with all of the Chaos Emeralds, the Sol Emeralds, or the Master Emerald. Super transformations first appeared in "Sonic the Hedgehog 2", where Sonic transforms into Super Sonic if all seven Chaos Emeralds and fifty or more rings are held at the same time. While in Super Sonic form, Sonic gains invincibility (except from instant-kill