Gameplay
Overall, the gameplay is similar to previous 8-bit Sonic games, albeit players can now play as either Sonic or Tails. For the first time in the 8-bit series, both characters are able to perform the Spin Dash introduced in the 16-bit version of Sonic 2. By holding up and pressing buttons, Sonic can perform the Super Peel-out introduced in Sonic CD, while Tails is able to fly, this being the first game in which he can do so. While playing as Sonic, players can collect rocket boots which allow him to fly through the air for a short time. He is also able to enter Special Stages. Tails is slower than Sonic and can't enter Special Stages or use rocket boots, but he starts the game with more lives and continues.
Unlike previous 8-bit Sonic games, the Chaos Emeralds are mostly located in Special Stages available while playing as Sonic. In order to enter a Special Stage, Sonic needs to collect 100 Rings in one act (the player also will be awarded an extra life for collecting 100 Rings). Successfully completing the Special Stage allows Sonic to collect a Chaos Emerald. Failing to complete the Special Stage will put Sonic to the next act, without the Emerald. Robotnik himself holds the sixth Chaos Emerald, and the player needs to beat him in order to win it back. Tails doesn't have the Emeralds as a concern for the player and beating the game yields the same ending, effectively making Tails an "Easy" mode.
Read more about this topic: Sonic Chaos