Successfully complete the game to unlock the bonus world at the top of the world map.
Collect all of the red rings in a zone to unlock a Chaos Emerald for that zone.
Play as Super Sonic
Collect all seven Chaos Emeralds to unlock Super Sonic. Then, collect 50 rings in a level, and tap the icon on the Gamepad to use Super Sonic.
Successfully complete the indicated task to unlock the corresponding level:
Successfully complete the game to unlock the Hard difficulty.
Defeat the final Boss to unlock the music player.