Chaos

Chaos 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 the altar of the Master Emerald. 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 0, but with each Emerald it absorbs, it transforms into a more powerful form named from the equivalent number of Emeralds, eventually becoming "Perfect Chaos" with all 7 Emeralds.

After the Echidna tribe attempts to steal the Chaos Emeralds, harming various Chao in the process, Chaos absorbs the negative energy of the Emeralds, becomes Perfect Chaos and causes chaos until being sealed inside the Master Emerald with Tikal. It is released thousands of years later in Sonic Adventure, so Dr. Eggman can use it to conquer the world. Chaos, still filled with…