Dark Gaia

Dark Gaia (ダーク・ガイア) is the main antagonist of Sonic Unleashed. A gargantuan monster (referred to by Professor Pickle as a hyper energy organism), the representation of darkness, night and destruction, who was released from the center of the planet by Dr. Eggman's Chaos Energy Cannon at the start of Sonic Unleashed. Eggman plans to use the power of the great beast in order to conquer the world and establish his Eggman Empire. It is what spawns the monsters that plague the world during the night stages of the game.

History
Dark Gaia, alongside Light Gaia (named Chip by Sonic), was born in the beginning of time. While Light Gaia were born as the incarnation of light and rebirth, Dark Gaia was born as the incarnation of darkness and destruction, and they served as each other's counterpart.

The two of them came to live on Earth in the planet's beginning, but Dark Gaia proved to have a dark desire to destroy this world. Light Gaia however, took upon the duty of protect the planet from Dark Gaia, and as such, Dark Gaia began a conflict with Light Gaia in a continuous cycle over the eons. In this cycle, Dark Gaia's purpose is to gather negative energy from the world while sleeping in the planet's core over millions of years. Once it had gather enough power it would emerge from the core and destroy the world upon its awakening in an event refered to as "the time of awakening", but would then each time be defeated by Light Gaia, who rebuilds the world and returns Dark Gaia to the core for it gather up negative energy anew, a process repeated since time began and continues to this day.

Some ten thousands years prior to Sonic Unleashed, Dark Gaia had just finished another cycle with Light Gaia and had returned to the planet's core to grow strong enough for the next confrontation. After sleeping for some ten thousands years however, Dark Gaia was suddenly awoken by Dr. Eggman with his Chaos Energy Cannon in an attempt to use its power to conquer the world. However, because Dark Gaia awoke prematurely when Eggman fired his beam, Dark Gaia could not support its own weight and Dark Gaia fell apart with its pieces scattering throughout the world, resulting in creating hordes of shadow monsters and its influence affecting people negatively. The only exceptions were Sonic the Hedgehog because his will was too strong, even in his Werehog form and Light Gaia because he is Dark Gaia's opposite. The other four unaffected are Amy Rose, Professor Pickle, Dr. Eggman, and Tails for unknown reasons.

Over the course of the game, Dr. Eggman devises a way to gather the pieces of Dark Gaia and reassemble Dark Gaia, giving him the power needed to finally build Eggmanland. After Sonic (in his Werehog form) defeats Dr. Eggman's Egg Dragoon in the massive Eggmanland, the reassembled Dark Gaia appears. Eggman orders it to attack Sonic, but Dark Gaia, not intending to follow his orders, swats him away. Dark Gaia then re-absorbs its lost power from Sonic, costing him his Werehog form (which appears to injure Sonic in the process), and completes itself, gaining three extra eyes. Dark Gaia then tries to attack them both, but Chip calls upon the power of Gaia and gathers the Gaia Temples to form a gaint stone creature called Gaia Colossus. Chip battles Dark Gaia while Sonic attacks his eyes. While they are doing this, Dark Gaia completely regains its lost power and matures, growing seven eyes, and four extra arms (although in the transformation sequence it is only shown growing two arms), becoming Perfect Dark Gaia. Sonic gathers the Chaos Emeralds and once again becomes Super Sonic. Gaia Colossus and Super Sonic battle in the center of the Earth. In the end, Super Sonic and Light Gaia defeat Dark Gaia's final form and put him back to rest. Super Sonic after the gruesome battle, faints from weakness but Gaia Colossus catches him safely. He sends Sonic back to the surface of the Earth as he is once again sealed inside the Earth along with Dark Gaia.

Powers and abilities
Dark Gaia is shown to be one of the most powerful beings, good or evil, to ever appear in the Sonic series, possibly only second or equal to Solaris. During the climatic battle against it, Dark Gaia was able to fight Super Sonic to the point where he ended up fainting from exhaustion, something no foe so far has been capable of, and at the same time, take on Light Gaia, a being who supposedly should be on the same level of strength as Dark Gaia itself. Additionally, Dark Gaia (as shown in its perfect form) is one of the few enemies that is able to hurt Sonic while he is in his super form.

As the sole reason for its existence, Dark Gaia has the natural ability to break an entire planet into pieces, which will eventually lead to the destruction of the planet itself. As a hyper energy organism, it is capable of shooting large beams of energy, where the strongest ones needs time to charge up, create small orbs of purple energy that shoots themselves at any enemy that comes too close and unleash a well of dark energy that can envelop a entire planet, bringing it into total darkness. It is also shown being able to use its large claws in hand-to-hand combat, and pick up large blocks of magma with its hands and throw them like meteors.

Since it is a physical manifestation of darkness, Dark Gaia can draw power from the negative energy in the world, allowing its power to grow stronger, which is necessary for it to reach maturity. Combined with its status as a energy being, the fragments of Dark Gaia is capable of creating various dark and destructive monsters that are capable of possessing people, causing negative and erratic behavior. Its energy can also cause beings or even the environment to transform into corrupted creatures, such as the Dark Gaia Phoenix, Dark Moray, Dark Guardian, or to a lesser degree, Sonic the Werehog. As shown by Eggman, Dark Gaia's energy is capable of powering machinery, such as the Egg Dragoon and Eggmanland.

Dark Gaia's only known weak spots are its various green eyes, which seems to be highly sensitive to damage, since Sonic, in his normal form, could inflict significant damage on Dark Gaia by attacking them. Also, because Dark Gaia in its first stage still is immature, it only uses its powers on a basic level, such as using it hands to pick up magma, rather than by levitation and can lose focus on its energy blasts, if attacked.

Battle
thumb|right|300px|The Dark Gaia battle in the 360/PS3 version.The battle with Dark Gaia varies between the game versions of Sonic Unleashed.

Wii/PS2
In the Wii & PS2 versions, Chip fights Dark Gaia immediately. When fighting the Gaia Colossus, Dark Gaia simply attacks with its claws while Chip dodges and counter-attacks with punches. This fight is generally considered akin to playing the Punch-Out! series of games, where Chip must counter, block or attack Dark Gaia. After the Gaia Colossus depletes Dark Gaia's Hit Points to zero, Sonic takes over and must run across the Colossus and clear a quick-time event to attacks one of Dark Gaia's eyes without time limit. Sonic does this runs consecutively three times before Dark Gaia is defeated and the story moves on to the battle with Perfect Dark Gaia.

Xbox360/PS3
In the Xbox 360 and PS3 versions of the game, the fight with the Gaia Colossus occurs a different way. The battle starts with Chip having the Gaia Colossus fly towards Dark Gaia from a distance to engage in the actual fight. During this time, Dark Gaia tries stop him by throwing massive molten rocks, which can be destroyed with the Gaia Colossus' fire punch, and firing a laser from its mouth, which cannot be avoided and must therefore be guarded against to minimize the damage.

Once reaching Dark Gaia, as opposed to a simple fist fight, Chip must attack Dark Gaia with a quick-time event. After clearing the quick-time event, Sonic takes over and tries to attack Dark Gaia's eyes by racing through the Gaia Colossus and then clearing another quick-time event. Unlike the Wii/PS2 version however, this course has a time limit as Chip is merely just holding Dark Gaia back so he cannot attack, with the time limit being the amount of time Dark Gaia has until he charges up his attack. If you do not get to the eye before the time limit, Dark Gaia fires its laser and you lose a life, so you must start over. If Sonic manages to attack one of its eyes however, Dark Gaia will throw Sonic and the Gaia Colossus away in pain, and the player has to start over, by trying to reach Dark Gaia again, resuming the process. This cycle has to be done three times before clearing the Dark Gaia boss battle and moving on to the battle with Perfect Dark Gaia.

Trivia

 * Dark Gaia resembles the second form of the final boss in the game Terranigma. In fact, the final boss in Terranigma is also called "Dark Gaia."
 * In the Wii/PS2 version when Sonic must attack Dark Gaia's eyes by going across the Gaia Colossus, it is the only time Sonic grinds in 3D, in this version all rails are strictly 2D only. It is also the only time when Sonic must use the quick step on a grind rail.
 * Sonic in his normal form actually inflicted a significant amount of damage on Dark Gaia before he became Perfect Dark Gaia.
 * The monsters that are made of Dark Gaia's essence somewhat resemble the Heartless from the Kingdom Hearts series of video games.
 * Dark Gaia also appears to be able to change the composition of its skin. In the cutscene when it transforms from Dark Gaia to Perfect Dark Gaia, its skin appears to be stretchy but firm, while the skin on the opposite side of its body appears to be brittle.
 * The name Gaia is derived from an ancient Greek goddess, who was the personification of the Earth. (A previous Sonic villain, Chaos, was also named after a Greek god.) Although named after a goddess, Dark Gaia is referred to as male.
 * Dark Gaia seems to change size throughout the course of Sonic Unleashed. When he is first awakened, he is large enough to put one hand on either side of the planet, yet during the final fight, he is noticeably smaller and fits inside the planet with plenty of extra space in the planet's core. This is probably due to Dark Gaia's mass being spread out and incomplete, as Orbot states later on.
 * Perfect Dark Gaia is the largest final boss in the series to date, being the size of a large continent.
 * Dark Gaia is the only boss in Sonic Unleashed with "Dark" as a prefix that is fought with normal Sonic. Also, the Egg Dragoon is the only Boss with "Egg" as a prefix that is fought with Sonic the Werehog.
 * Dark Gaia is the reason that Sonic Unleashed was given the ESRB rating of E10+, as he leaks green blood during his transformation into Perfect Dark Gaia. This blood is also seen in his "death" scene.
 * Other than Sonic, the only other beings Dark Gaia could not affect were Chip, Dr. Eggman, Tails and Amy.
 * Dark Gaia's power, as explained by Professor Pickle, is drawn from hatred and sadness manifested by the people on the planet.
 * In Sonic Adventure 2, Tikal's earthquake attack was called "Wrath of Gaia". This is most likely a coincidence.
 * Dark Gaia could arguably be considered neutral since its natural role is to destroy the world.
 * All of the bosses in the game with a Dark prefix appear to elemental:
 * Dark Gaia Phoenix - Fire
 * Dark Moray - Ice
 * Dark Guardian - Wind and/or Thunder
 * Dark Gaia - Earth
 * If you look closely during the third round with Dark Gaia in the Xbox/PS3 version of Sonic Unleashed it appears as if Dark Gaia laughs.
 * Dark Gaia appears to have a resemblance to Iblis. Dark Gaia has Shadowy dark minions like Iblis has Fire minions, and they both have a desire to destroy the world. They are also gods of destruction.