Classic Sonic's world

Classic Sonic's world is a location that appears in the Sonic the Hedgehog series. It is the home dimension of Classic Sonic, and an alternate reality derived from the dimension of Modern Sonic's world. It is noticeable for being a near-perfect duplicate of Sonic's dimension, except for a few key differences.

Description
Classic Sonic's world is a near perfect reflection of Sonic's dimension, possession several of the same distinguished locations, like Angel Island and Little Planet, and several of the same inhabitants, like Sonic the Hedgehog and Dr. Eggman. The history of Classic Sonic's world likewise closely follows the history of Sonic's dimension, having experienced many of the same events, like the West Side Island incident and the Angel Island Incident. However, it also has a few events exclusive to itself, like its own Phantom Ruby incident; it is these events that separates it from its counterpart.

While their timelines appear almost identical, Classic Sonic's world appears to be set in the recent past of Sonic's dimension.

Past
The past of Classic Sonic's world was most likely largely the same as the past of Sonic's dimension.

Sonic Generation
In Sonic Generations, some time between the West Side Island incident and the Phantom Ruby incident, Classic Sonic's world got invaded by Modern Eggman and the Time Eater, who began erasing events from this world's history. This was an event that did not occurred in Sonic's dimension.

The emergence of the Time Eater sent Sonic and Tails into the White Space. There, they teamed up with Modern Sonic and Tails to stop the Time Eater. Meanwhile, Modern Eggman went back in time to recruit Dr. Eggman from the Death Egg for his scheme to rewrite history in their favor. However, the Eggmans were stopped by the Sonics, which undid the damage it did to Classic Sonic's world. In the aftermath, Sonic and Tails returned to their world.

Sonic Mania
In Sonic Mania, some time after saving Angel Island, the Phantom Ruby showed up on Angel Island. Detecting the jewel, Sonic and Tails tried to secure it, only for Eggman's Hard Boiled Heavies to do it first. The jewel would soon after transform the Hard Boiled Heavies, causing them to go rogue. Despite this, Eggmaan managed to obtain the Phantom Ruby. Teaming up with Knuckles, Sonic and Tails set out to get the Phantom Ruby away from Eggman.

On their adventure, Sonic and his friends would fight several robots, the Hard Boiled Heavies, Metal Sonic and Eggman, while collecting the Chaos Emeralds. Eventually, the trio cornered Eggman on a re-mechanized Little Planet, where they defeated him. While Tails and Knuckles escaped Little Planet before it vanished, Sonic had an extra showdown with Eggman and the Phantom King that got him and the Phantom Ruby sent to Modern Sonic's world.

Inhabitants

 * Dr. Eggman
 * Knuckles the Echidna
 * Metal Sonic
 * Miles "Tails" Prower
 * Sonic the Hedgehog

Trivia

 * If the theory about many-worlds interpretation, which says that one will create an alternate reality when changing the past, applies here, then Classic Sonic's world may have split off from Sonic's dimension and become an alternate dimension when Dr. Eggman tried to change the past back in Sonic Generations. This would explain why Classic Sonic went from being a past version of Sonic in Sonic Generations to be an alternate reality counterpart of him in Sonic Forces.