Chaos Emerald (Classic Sonic's world)

The Chaos Emeralds (カオスエメラルド) are objects in the Sonic the Hedgehog series. They are alternate versions of the Chaos Emeralds from another dimension set in the recent past. Like their counterparts, they are seven ancient emeralds with mystical powers.

Overview
In Sonic Mania, the Chaos Emeralds were collected by Sonic, Tails, Knuckles over the course of their adventure. When Sonic got transported to the Egg Reverie Zone, where Dr. Eggman fought the Phantom King over the Phantom Ruby, Sonic used the Chaos Emeralds to go Super Sonic. After delivering the final blow to the villains, the Chaos Emeralds separated from Sonic (thus returning Sonic to normal) and reacted to the Phantom Ruby, which prompted the ruby to take Sonic and itself through a worp to another dimension while the Emeralds scattered.

In gameplay, the seven Chaos Emeralds can be obtained by clearing Special Stages. Within these stages, UFOs can be seen carrying around their respective Chaos Emerald. If one of the playable characters in the game (Sonic, Tails or Knuckles) collects all seven Emeralds, they will be able to enter their respective Super State in normal gameplay. In Sonic's case, collecting all seven Emeralds will also enable the player to enter Egg Reverie Zone as Sonic, where the final boss of Sonic Mania is fought, after clearing Titanic Monarch Zone. Defeating the final boss will in turn unlock the true ending of Sonic Mania.