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Perfect Dark Gaia is the fully matured form of the Dark Gaia, which it gains after gathering all of it's energy from across the planet.
Every ten thousand year since time primordial, Dark Gaia has achieved this form when emerging to destroy Sonic's World, only to engage Light Gaia in a fight that lasts for centuries. At the end, Light Gaia seals Dark Gaia and himself in the planet's core where they rest until their next battle. (StH: #259, #286)
Shattered World Crisis
When the world broke apart from the excess energy of the Super Genesis Wave, Dark Gaia was unable to obtain maturity due to it's premature awakening. Instead, It's power was scattered across the broken planet and either effected people in a negative way, or formed into monsters that terrorize the night. However, Dr. Eggman desire to have all of the Dark Gaia's energy for himself and created Eggmanland and the Summoning Spire to gather and harness it as a fuel source. Eventually, the spire collected enough energy for the Dark Gaia to assume it's imperfect physical form and destroyed Eggmanland as it emerged from the planet's core. After drawing on it's remaining power to fully mature into it's perfect form, Dark Gaia was forced to fight the combined forces of Super Sonic and the Gaia Colossus, who were able to defeat Perfect Dark Gaia and seal in the planet's core again after an epic battle. (StH: #286, #287)
Being at the peak of its strength and capabilities due to having regained its full power, Perfect Dark Gaia can generate a forcefield via its serpent-like growths that even Super Sonic could not penetrate. Perfect Dark Gaia possesses as well immense endurance; it could withstand most of the attacks from both Super Sonic and the Gaia Colossus. It also has great strength, enough to completely immobilize the Gaia Colossus in its grip and deal hefty blows with its sharp claws. It can also fire an immense energy beam from its central eye which packs enough power to bypass Super Sonic's nigh-invulnerability.
- Perfect Dark Gaia at Sonic News Network