Phantom Ruby

The Phantom Ruby (ファントムルビー), also known as the mysterious gemstone, is a recurring object in the Sonic the Hedgehog series. It is an interdimensional gemstone of incredible power that was fought over by several parties across multiple dimensions. It plays a central role in Sonic Mania and its follow-up game Sonic Forces.

Appearance
The Phantom Ruby is a magenta icosahedron ruby with black ripple patterns along its surface. It is also small enough to fit in the palm of a hand.

Powers and abilities
While different from the Chaos Emeralds, it is still remarkably powerful and has been theorized to be a source of unspeakable power. When channeling its power, the Phantom King became powerful enough to bypass a Super State's invulnerability. Similarly, the ruby itself can also restrain the Chaos Emeralds and depower a Super State. Its power is as well so great that it could affect the Master Emerald's ability to keep Angel Island afloat, causing the island to fall back into the ocean. The Phantom Ruby's abilities are said to outclass even those of the Master Emerald's. Because of its massive amount of power, it was implied that the Phantom Ruby's mere presence at the heart of the Eggman Empire was such that Eggman could afford to have a comparatively small amount of his own forces stationed at Metropolis, provided the gem was at full power.

The Phantom Ruby's exact powers are based on virtual reality control. It takes control of people's visual and depth perception to feed false information to the brain creating a new reality for them. This includes empowering and altering beings (like the Hard Boiled Heavies and Infinite) or creating illusory places and entities that feel real. Its powers can also warp the fabric of space-time, allowing it to create pocket dimensions such as Egg Reverie Zone and Null Space, as well as teleport entities from place to place. When used alongside the Chaos Emeralds' time-space powers, it transported Classic Sonic and itself to another dimension.

When touched, the Phantom Ruby, as a default, seems to generate whatever the person who touched it most desires, although these only last as long as it is being physically touched by the person. For example, when Infinite accidentally touched the gem, he was struck by images of a destroyed world of chaos, based on his own violent desire for change.

When used, the Phantom Ruby creates a by-product known as the Ruby Mist, a mist-like substance that distorts space-time within it.

Sonic Mania
In Sonic Mania, the Phantom Ruby appeared on Angel Island after a dimensional breach occurred in the atmosphere, its effects causing Angel Island to fall into the sea again. Its unique energy signature was soon detected by Sonic the Hedgehog and Miles "Tails" Prower who went to investigate it. Also detecting the gemstone was Dr. Eggman, who sent his team of elite Egg-Robos, the Hard Boiled Heavies, to retrieve it after theorizing its potential.

When Sonic and Tails arrived on Angel Island, the Hard Boiled Heavies were excavating the Phantom Ruby from the ground. As they did so, the gem warped space-time around them and catapulted Sonic, Tails, the Hard Boiled Heavies, and Knuckles the Echidna (who was relaxing nearby) to Green Hill Zone. In the process, the Phantom Ruby transformed the Hard Boiled Heavies into more powerful Egg-Robos with wills of their own.

The Hard Boiled Heavies promptly escaped with the gem which was soon taken by Dr. Eggman, whose usage of the gem sent Sonic and co. away when they caught up to him. When the trio later cornered Eggman in Press Garden Zone, the doctor used the ruby to sent them to Little Planet.

Eggman ultimately made the Phantom Ruby the power source of his Titanic Monarch, its power distorting space within Eggman's creation. When Sonic and co. faced Eggman, the doctor used the gem to power a battlesuit. Upon Eggman's defeat, the Phantom Ruby pulled the doctor and Sonic into a strange space where Eggman and the traitorous Phantom King fought over the gemstone, only for Super Sonic to defeat them both. In the aftermath, the Phantom Ruby reacted to Sonic's seven Chaos Emeralds, causing Sonic and the ruby to be pulled through a spatial warp to another dimension.

Sonic Forces
Several months prior to Sonic Forces, the Phantom Ruby (though it had no name at the time) was found by Dr. Eggman after the sensors of his Arsenal Pyramid detected an unusual energy signature outside, prompting Eggman to investigate. Upon touching the Ruby, Eggman had a brief vision of Eggmanland. Intrigued, Eggman researched the jewel, eventually coining the name "Phantom Ruby". However, his base was soon attacked by the Jackal Squad, led by the ultimate mercenary. During the attack, Eggman inadvertently used the Ruby to materialize a troop of Egg Pawns to exterminate the squad. The ultimate mercenary then tried to kill Eggman, but struck the Ruby instead, causing him and Eggman to see a ruined world based on the former's own violent desire for change. Impressed with the mercenary, Eggman got him to join his empire so they could achieve their mutual goals.

Seeking to test the Phantom Ruby, Eggman went to Angel Island where he used it to create an illusion of the Pachacamac's village and have Knuckles and Silver fight a replica Chaos. Although Knuckles and Silver overcame the replica, Eggman deemed the test to be a success. Eggman would afterward analyze the Phantom Ruby in his lab in Mystic Jungle in hopes of using it to take over the world. Using the data he gathered, Eggman created several defective "Phantom Ruby prototypes" which he used to experiment on until he created a finalized prototype. That prototype was given to the ultimate mercenary, who, after a humiliating loss to Shadow, cast away his previous identity and assimilated with the prototype after a number of experiments, becoming Infinite. Under the direction of Eggman, Infinite sought to destroy the world with the Phantom Ruby and allow the Eggman Empire to rise to power.

While the original Phantom Ruby remained in Eggman's possession, he and Infinite put their plans into action by using the finalized Phantom Ruby prototype to take over more than 99% of the planet, sparking the War to Take Back the Planet. Six months later however, the Resistance discovered that the Phantom Rubies relied on the Death Egg to provide them with the power they needed to work. As such, the Resistance destroyed the Death Egg, weakening the Rubies. However, Eggman had anticipated this, and had a backup power reactor built underneath the Eggman Empire Fortress.

At the climax of the war, the Resistance destroyed the backup reactor. Having anticipated this however, Eggman incorporated the original Phantom Ruby into his Death Egg Robot and its energy supply (making it an "invulnerable ruby") in an effort to crush the Resistance. By recklessly overclocking the Phantom Ruby, Eggman granted his Death Egg Robot powers beyond Infinite's, allowing it to create thousands of replicas to combat the Resistance with. During the Death Egg Robot's battle with Sonic, Classic Sonic and the Avatar however, the Phantom Ruby got destroyed by the trio, which undid all it had wrought.

Trivia

 * The sound effect made by the Phantom Ruby when it distorts space-time is the same as the one Infinite's cube attack makes in the Sonic Forces E3 Trailer. Extracted sound data from Sonic Mania reveals that the sound file's names for the sound effect were "RedCube_R" and "RedCube_L", further hinting at a connection between the Phantom Ruby and Infinite. Similarly, when it reacted to the Chaos Emeralds after the final boss in Sonic Mania, it briefly exhibited a cube-based distortion aura like Infinite's in the "Enter Infinite" trailer for Sonic Forces.
 * Sonic also poses the exact same way as in the reveal trailer for Sonic Forces after the Phantom Ruby warps him somewhere. This has led many fans to believe that the ending of Sonic Mania may tie into Sonic Forces, which was later confirmed by Takashi Iizuka during the Tokyo Game Show 2017.
 * Prior to officially being named by Dr. Eggman, Cubot proceeded to suggest names for it such as the Spooky Sapphire, Anarchy Beryl, and Precious Stone, with Orbot rejecting the names for various reasons (specifically, that it didn't shine blue, that it was too derivative, and it was from the wrong game, respectively). The latter two names were a reference to the Anarchy Beryls of anti-Mobius from the pre-Genesis Wave continuity of Archie Comics' Sonic storyline and the Precioustone from Sonic Shuffle, respectively.