Master Emerald

The Master Emerald is a massive, green Chaos Emerald that keeps Angel Island afloat. It was created by the combined might of Athair and the Brotherhood of Guardians, during a confrontation between Super Sonic, Hyper Knuckles, Turbo Tails and the recently empowered Mammoth Mogul. The Master Emerald contains the powers of the twelve individual Chaos Emeralds which formerly held Angel Island afloat. Since its creation it has been used by heroes and villains alike.

Creation
When Mammoth Mogul stole the power of 11 Chaos Emeralds from the super being Enerjak, he transported Sonic the Hedgehog, Tails and Knuckles the Echidna to an alternate Zone. They managed to escape the zone however, and the powers of Power Rings, Sonic and Knuckles transformed into Super Sonic and Hyper Knuckles, while Tails managed to transform into Turbo Tails with the help of Athair and the Ancient Walkers. With their combined powers along with help from Athair and the Brotherhood of Guardians, Master Mogul's powers were utilized and transformed the power of the numerous Chaos Emeralds into a single Master Emerald, with Mogul trapped within. This new massive Chaos Emerald was then used to maintain Angel Island's low orbit of the planet Mobius. (StH: #56, KtE: #9)

Sought Out By Villains
After Dr. Eggman liberated Chaos from the Black Emerald, he proceeded to attack the Floating Island with a legion of Shadowbots and the Egg Carrier while the Brotherhood of Guardians' defences were still down due to tampering from Hunter. The Master Emerald was shattered, and pieces of it were used to help sustain Chaos in his weakened state. Eventually however, Knuckles was able to locate and retrieve all of the pieces of the shattered Master Emerald, with the Brotherhood providing a new alter for it to better harness its magical powers. (StH: #79, #80, #81, #84)

During the surprise invasion by the Eggman Empire after the Xorda attack was fended off, the Brotherhood of Guardians (sans Locke) fought off an entire army of Egg Pawns in defence of the Master Emerald, while the rest of the island was simultaneously attacked by the combined forces of the Eggman Empire and the Dingo Regime under the new leadership of Kage Von Stryker, who had allied with Dr. Eggman. The Brotherhood managed to successfully defend the Master Emerald, but were subsequently captured in their weakened state by Dr. Finitevus. Locke managed to successfully protect the Master Emerald on his own, until after Sonic's return, when he was forced to turn its protection over to the Dark Legion when its location was discovered. Locke was captured while the Dark Legion safely moved it. Eventually, the Master Emerald played a pivotal role when it restored Knuckles' lost Chaos-based powers and transformed him into Super Knuckles and allowed him to kill Hunter. The Master Emerald was then re-located once again, with Locke protecting it from harm. (StH: #139, #140, #141)

Some time later, Evil Sonic, with help from Rouge, attempted to steal the Master Emerald. While Rouge distracted Locke, Evil Sonic managed to get into the chamber, but was soon stopped when he faced off against Sonic Prime, who had returned from Anti Mobius. Locke sent Anti Sonic flying away when he realized which was the real Sonic, and went back to protecting it. (StH: #150, #151)

Rouge and Evil Sonic later returned, and while the two fought against Locke directly, they were able to get closer to the Master Emerald. Evil Sonic managed to get onto the Master Emerald while Rouge fought with Locke, and began to transform. His transformation was stopped mid-way, altering his appearance into green, whereupon he took on the name Scourge. Scourge then defeated Locke, and used the Master Emerald to use Chaos Control to teleport himself and Rouge away. (StH: #160, #161)

The Great Harmony
When A.D.A.M. enacted his plan to draw all of the Chaos Emeralds from around the universe to Mobius, his plans ultimately allowed Tails, the "Chosen One", to fulfil the prophecy of producing the Great Harmony. While A.D.A.M. was distracted, Shadow assisted Tails and opening a portal to the Zone of Silence. There, Tails sent all of the Chaos Emeralds where they would be safe and out of reach from villains, thus fulfilling the prophecy set out by the Ancient Walkers. When A.D.A.M. was using a captured Shadow and Tails to pull all of the Chaos Emeralds to Mobius, he was perplexed as to why the Master Emerald was not amongst them. The combined effort of Locke and Dr. Finitevus ensured the Master Emerald remained secured on Angel Island. (StH: #169)

Return of Enerjak
Not longer after the Great Harmony, Dr. Finitevus managed to con Locke into entrusting him with the care of the Master Emerald while he searched for the Brotherhood of Guardians. During Locke's absence, Finitevus enacted the final phases of his ultimate plan to destroy Mobius by reviving Enerjak and placed a Hex on the Master Emerald. When Knuckles the Echidna returned to Angel Island to assist his father Locke in protecting the Echidnas, he was ambushed by the Destructix and brought before Finitevus. The mad scientist informed him of the destruction of Albion and how many echidnas were alive. With this as persuasion, Finitevus convinced Knuckles to pull energy from the Master Emerald and become Enerjak. The moment he did this, Knuckles became a slave to Finitevus' hex, making his ideals bend to those of the albino Echidna. (StH: #171, #181)

When Sonic and Julie-Su arrived on the scene, Finitevus informed them that no one could use the power of the Master Emerald except for Knuckles due to the hex he placed on it. Despite this, Sonic some how managed to use its power to turn into Super Sonic. Which this power, Sonic managed to distract Knuckles (who was presently Enerjak) long enough for Locke to surrender his life and thereby break the hex Finitevus placed on the Master Emerald. With the hex broken, Knuckles returned to normal and forced Finitevus to flee. Since then, Knuckles has vowed to protect the Master Emerald, even if he must do it alone. (StH: #183, #184)

Shrine Isle
Having been separated from the mainland of Angel Island by the battle between Super Sonic and Enerjak, the Master Emerald Shrine now floats a short distance away. The Chaotix bridged this gap during a trip to the island to check up on Knuckles, during which Rouge the Bat convinced the Guardian that he could watch over the Master Emerald and continue to take part in the war against Dr. Eggman without choosing one or the other by using a Warp Ring taken from Dr. Finitevus. (StH: #186)

Later on, the Master Emerald was fought over by Espio and Knuckles. The fight ended when Espio told Knuckles he had conflicting orders and couldn't complete his mission. (StH: #203, #204)

Vector the Crocodile and Ray the Flying Squirrel later took guard duty over the Emerald while Knuckles went on another mission. Ray managed to grill Vector and learned a little bit about his past. Right after that, they were attacked by what looked to be new models of the Wing Dingo's. They then attempted to fight off the hordes of robots and keep them away from the Emerald. (SU: #9, #10