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 an almost exact 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, having the same distinguished locations, like Angel Island and Little Planet, and 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, Classic Sonic's world has witnessed a few events exclusive to itself, like its own Phantom Ruby incident; it is these events that differentiate it from its counterpart.

While their timelines appear almost identical, Classic Sonic's world is a couple of years behind Sonic's dimension. The inhabitants of Classic Sonic's world are therefore younger than their counterparts in Sonic's dimension, and some events in Sonic's dimension have yet to transpire in Classic Sonic's world.

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

Sonic Generations
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. This was an event that did not occur 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 Modern Tails to stop the Time Eater. Meanwhile, Modern Eggman went back in time and recruited Dr. Eggman from the time of the first Death Egg for his scheme to rewrite history in their favor. However, the Eggmans were stopped by the Sonics, which undid the damage the Time Eater had done 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, Eggman managed to obtain the Phantom Ruby. Teaming up with their new ally Knuckles, Sonic and Tails set out to get the Phantom Ruby away from Eggman.

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

Sonic Mania Adventures
Returning from Modern Sonic's world, Sonic arrived on Angel Island, which had been dug up by someone. Sonic was soon after lured into a trap by Dr. Eggman, but the hedgehog managed to turn the situation around with the Chaos Emerald he had and get Eggman stuck in the trap while he escaped. Along the way, Sonic discovered that Eggman was on the hunt for the Chaos Emeralds, and that he already had four of them.

Locations

 * Earth
 * Angel Island
 * Hydrocity Zone
 * Lava Reef Zone
 * Press Garden Zone
 * South Island
 * Green Hill Zone
 * West Side Island
 * Chemical Plant Zone
 * Mirage Saloon Zone
 * Oil Ocean Zone
 * Studiopolis Zone
 * Little Planet
 * Metallic Madness Zone
 * Stardust Speedway Zone
 * Titanic Monarch Zone

Inhabitants

 * Animals
 * Flicky
 * 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 became 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 being an alternate reality counterpart of Sonic in Sonic Forces.
 * There might be more characters inhabiting this dimension, such as Amy Rose and Fang the Sniper, as proven by their cameos in Sonic Mania, although this is unconfirmed.
 * While the Classic counterparts of Sonic, Tails, Dr. Eggman, and Metal Sonic made their first appearance in Sonic Generations, Knuckles' counterpart did not, making his official debut in Sonic Mania. The reason for this is unknown.