The game follows Sonic and his friends as they travel through various zones in order to stop Dr. Eggman from taking over South Island. The game features four playable characters; Sonic, Tails, Knuckles and Amy. Each character has the same moveset as they did in Sonic the Hedgehog 3 and Sonic & Knuckles, with the addition of a melee attack. Each character has a special ability, such as Sonic's splice shield, Tails' flight and Knuckles' gliding and climbing abilities. In her playable 2D debut, Amy cannot perform the Spin Dash or get into ball form when jumping like the others, and must rely on her Piko Piko Hammer to defend herself, making her unique amongst the characters. Grind rails first introduced in Sonic Adventure 2 also make their first 2D appearance. Sonic and Tails can also be used at the same time during the story by inputting a cheat code at the character selection screen. When playing as both characters, the gameplay is similar to that of Sonic the Hedgehog 2: The player can only control Sonic and a CPU-controlled Tails follows him.