Chaos 0

(also known as Chaos 0) is the main antagonist in the video game Sonic Adventure for the Sega Dreamcast. Chaos is an immortal, ageless god-like creature that seems to be composed entirely of water (ironically Sonic has a weakness of water), but is also said to be concentrated Chaos Emerald energy (in Sonic X, Doctor Eggman implies that it is composed of "Chaos energy in a liquid state"). It was trapped inside the Master Emerald for thousands of years before being released by Dr. Eggman in a bid to conquer the world. It was also the original guardian of the Chaos Emeralds, Chao, and the Master Emerald. In Sonic Adventure it absorbed the negative energy of the Chaos Emeralds to attain its final and strongest form.
Chaos was originally a good natured Chao. Contact with the positive energy of the Chaos Emeralds transformed it into a water-like creature. It used the power to guarantee clear water around the altar of the Master Emerald, and to protect its fellow Chao. However 4,000 year ago, the leader of the Echidna tribe, Pachacamac, tried to steal the Emeralds so he could use them against his enemies. His warriors stormed the shrine where the Emeralds were, harming many Chao in the process. Chaos, in a fit of rage, absorbed the negative power of the Chaos Emeralds, and transformed into Perfect Chaos. The resulting floods destroyed the civilization. Pachacamac's daughter, Tikal, linked her consciousness with Chaos's via prayer, and sealed them both into the Master Emerald. It is from this point in history that the emeralds were called "Chaos Emeralds". Nobody knows what happened to the Emeralds after that.Chaos's next appearance is in Sonic Battle, where Knuckles the Echidna claims that Chaos appears when there is an upcoming disaster. When Dr. Eggman threatens the Earth with his Death Egg in the final story, a nearby volcanic crater is flooded, and Chaos emerges. It can then be challenged by the player. Chaos is the strongest playable character in the game (Minus Emerl as he is customizable), but also by far the slowest.
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Chaos appears, as Perfect Chaos, in Mario And Sonic At The Olympic Winter Games as an obstacle in Dream Figure Skating(Sonic World). He also appears in is normal form as a VIP character, that will sometimes send you letters, and as a sticker.
Chaos' form and skills change and increase with every Chaos Emerald that it absorbs. Over time it develops from a humanoid water creature to a horrible, world-destroying monster.
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This is the base form of Chaos before it has absorbed any Chaos Emeralds. It is humanoid, and about five feet tall with bright green eyes. Its brain is visible in this form through its watery exterior. Sonic Adventure begins with Sonic fighting Chaos 0 outside the City Hall in Station Square. Its attacks include extending its arms to punch, spinning around with its arms extended and jumping high and quickly onto light posts in order to get out of Sonic's range.
In Sonic Adventure 2, Chaos Zero (as it is called in-game) is a secret character that can be unlocked by getting all 'A's in Rouge's missions. After that, it will be playable as a treasure hunter in 2-Player Mode. In Sonic Adventure 2: Battle, Chaos Zero is an initially available character. It is a very slow character, but has powerful attacks. In this game, Chaos Zero can glide, climb and dig just like Knuckles and Rouge, and it also gains three new attacks: Chaos Impact, a powerful ground punch that creates a small earthquake, Chaos Strike, a blue energy pulse that harms and confuses enemies, and Chaos Bind, a move which freezes the air around the enemy for 30-40 seconds. Chaos Zero is also able to swim underwater for an unlimited amount of time.
After Chaos appears in Sonic Battle, Emerl can challenge it and copy its abilities. After the player defeats Chaos, it is unlocked as a playable character in Battle and Challenge modes. In-game, Chaos is the slowest character in the game but its extendable limbs give it a much wider attack range than it appears to have, and it is very powerful. It can turn into puddle of water as usual, and can create fountains, tentacles, and orbs of water.http://
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After Chaos absorbs one Chaos Emerald, it is virtually unchanged except for a line of bones that travel down its right arm into its hand, where the Emerald is located. As such the arm becomes bulkier. He briefly appears in Sonic Adventure after Sonic or Tails fights Eggman for the first time, and is never fought. Due to never being fought, his abilities are unknown. Knuckles also meets Chaos 1 in the Hotel room just before it transforms into Chaos 2.
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Chaos is much stronger after absorbing two Emeralds. It is taller and more muscular. The bones that were in Chaos 1's right arm now run along both of Chaos 2's arms and now both hands have Emeralds. Its head has moved forward, giving it a more unpleasant appearance, the horns on his head have also changed position to give it a hammerhead style look. It has also developed new powers like a blue energy shield to prevent frontal attacks and the ability to transform into a huge ball, several small orbs, or waves of water. Knuckles the Echidna fights it in the Hotel Restaurant in Station Square. Sonic, Knuckles and Miles "Tails" Prower later meet Chaos 2 by the pool of water in the Mystic Ruins just before it becomes Chaos 4.
In Sonic X, Sonic and Knuckles fight Chaos 2 together right after Sonic defeats Chaos 0. In this version of the fight, Chaos sprays water from his hands and has a near-unbreakable shield of electrical properties.
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Chaos 3 was never shown in Sonic Adventure due to the circumstances of absorbing two Emeralds at once. This causes it to skip this form, but, presumably, he does have this form.
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Chaos changes considerably after absorbing four Chaos Emeralds. It is now a huge shark-like creature with razor like fins. It fights Sonic, Tails and Knuckles in a small pond in the Mystic Ruins, but is defeated. Its new powers include being able to fire energy waves, swimming at high speeds, creating water explosions, and turning into four balls that bounce toward the player. If Chaos 4 is out of water it simply floats in the air. The third and fourth Emeralds Chaos absorbed are now located in its belly. Big the Cat encounters Chaos 4 on the Egg Carrier just before it transformed into Chaos 6. Interestingly, even though Chaos' tail is absorbed by Froggy at the time being, Chaos 4 still sports a tail in which he can use for attack.
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This form is never seen in the game due to the fact that Chaos 4 had absorbed 2 more Chaos Emeralds at once, skipping this stage and moving to Chaos 6, although lacking its tail.
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After absorbing six Emeralds, Chaos has changed dramatically once again. It is no longer even vaguely humanoid, but a twenty-five foot tall scorpion-like creature. It also has eight or more eyes, a bulldog-like head and a mouth filled with razor sharp teeth. Its tail is tipped with a pendulum type blade. Unlike its previous forms, Chaos 6 cannot be injured by attacking its head, as the brain is too deeply situated to be damaged. (Interestingly, in Sonic X, Sonic and Knuckles work together to defeat Chaos 6, with Knuckles scooping away Chaos' body with Shovel Claw, and Sonic spin dashing straight through the exposed brain.) Instead, Chaos 6 can only be damaged by freezing and shattering its liquid body. Both Sonic and Knuckles fight Chaos 6 on the Egg Carrier and Big the Cat fishes Froggy out from inside Chaos. Chaos's new powers include creating powerful shock waves and trying to inhale enemies to eat them. He can also make dozens of spikes stick out of his body and smash enemies with his huge tail. The Emeralds it absorbed are now all around its body.http://
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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's 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. It 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 failsafe in case Chaos rebelled.
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.
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's 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's positive super form simply looked like an over sized version of Chaos 0 with the seven Emeralds in its forehead.
Later in the Sonic X comics, Eggman used the Emeralds and three robots, one with water powers, one with wind powers, and one with solar energy, combined with Chaos 0 to form Perfect Chaos, but with a robotic armor on its central torso. It once more wreaked havoc on Station Square before being stopped by Super Sonic, who smashed the controller Eggman was using to control Chaos and the armor, but not before it promptly struck Eggman's hovercraft, sending it flying. Restored, Chaos then went back to Angel Island, and presumably merged back with the Master Emerald.