Perfect Chaos

Perfect Chaos is a form of Chaos and the final boss of Sonic Adventure. Chaos takes this form after absorbing the negative energies of all seven Chaos Emeralds, Chaos will become a giant snake-like beast with a mouth extending far beyond its eyes, which for the first time have pupils that resemble a reptile's. At the base of its snake-like body seems to be a huge whirlpool and cyclone. It has large tentacles extending from its base.

Perfect Chaos' new powers include creating small tornadoes, firing clusters of yellow and pink fireballs, and firing a huge energy beam from its mouth. It has total control over water as Perfect Chaos is able to flood Station Square with ease.

Sonic Adventure
Perfect Chaos is the final boss in Sonic Adventure, where only Super Sonic has the power to take it down. In its Perfect form, Chaos was quickly able to shoot down Eggman's Egg Carrier 2, which was a fail-safe in case Chaos rebelled.

It should be noted that Perfect Chaos' energy beam has an uncanny resemblance to Godzilla's Atomic Ray and that Perfect Chaos himself looks like Godzilla's rival Biollante. Also the fact that it destroyed a city may have led Sonic Team to giving it resemblances to kaiju. It is said that Perfect Chaos is Chaos' negative super form. In the Sonic X comic book, in which it absorbed the positive energy of the emeralds to take down Eggman's mecha, Chaos' positive super form simply looked like an over sized version of Chaos 0 with the seven Emeralds in its forehead

Mario & Sonic at the Olympic Winter Games
Perfect Chaos makes a cameo as an enemy in Mario & Sonic at the Olympic Winter Games during the Dream Figure Skating competition.

Sonic Generations
Perfect Chaos serves as a boss in the game Sonic Generations, and is the main boss of the Dreamcast era. The player does not use Super Sonic in this game as the player cannot obtain all seven Chaos Emeralds before fighting it. Instead, the player must navigate three different kinds of levels before fighting it in its last resort, which is sending platforms out of the water. These platforms fall after an allotted time, so the player must hurry and avoid falling off. Strangely, Perfect Chaos has a much larger and more solid appearance than before.

Sonic X
In Sonic X, Perfect Chaos looks more like the Loch Ness monster due to an increased "back" size and several new tentacles. Perfect Chaos also uses a few more powers, like absorbing projectiles like a sponge and then spitting them back at the attacker through its mouth, using its tentacles to attack (he is seen splitting skyscrapers in half with them), and creating crystal spires and an energy shield. He also controls water and, if you look closely before his battle with Super Sonic, his tongue is much longer than his enormous jaws. He can also fire an energy beam, which he uses to burn the Egg Carrier 2 to cinders.