Chaos

Chaos (カオス, Kaosu ?) is a Chao mutated by the Chaos Emeralds that acts as a guardian for its species, protects the Master Emerald, and provides clear water around its altar.[41 ] It is a water-like being that can easily manipulate its body, allowing it to stretch limbs or liquefy itself. Without any Chaos Emeralds, it is known as "Chaos Zero", but with each Emerald it absorbs, it transforms into a more powerful form, eventually becoming "Perfect Chaos" with all 7 Emeralds.

It's first appearance is in Sonic Adventure, where Dr. Eggman attempts to use it to conquer the world. Chaos tracks down the emeralds, becomes "Perfect Chaos", and floods all of Station Square, but is ultimately defeated by Super Sonic. It reappears in Sonic Adventure 2 as a bonus multiplayer character and in Sonic Battle as a playable fighter. He reappears in his perfect form in Sonic Generations as a boss where he has a new look with green teeth and dark blue reptilian skin for the upper half of his body.[42 ] This was supposed to be how he always looked, but the technology of the Dreamcast at the time made this look impossible.[43 ]