Secret Stage Mode
After complete all seven special stages, return to the main menu and press Up, L, Down, R, Right, Left.
Play as Knuckles and Tails. Have Knuckles as your lead and when you face Eggman, use Knuckles' glide. Having Tails as your partner will give Knuckles more elevation on his glide, allowing you to hit Eggman's weak spot without any elevation help from the hands or the balls that fly around.
Sonic The Hedgehog Reference
In Zone 2, Sunset Hill, the music that plays is a remix of Green Hill Zone from Sonic The Hedgehog.
Play As Amy
Start a new game and successfully complete all three Acts of Toy Kingdom Zone to unlock Amy.
Play As Cream
Start a new game and successfully complete all three Acts of Cyber Track Zone to unlock Cream.
Play As Knuckles
Start a new game and successfully complete all three Acts of Sunset Hill Zone to unlock Knuckles.
Successfully complete the game. You do not need all the Chaos Emeralds. The "Sound Test" option will appear just above "Delete Game Data" in the options menu.
Boss Time Attack
Successfully completed the game. Do not have all Emeralds but have a Golden Ring in all stages (Act 1, 2, 3 and vs. Boss).
Short-cut for Zone:4 Act:2
When you're at the part below the Turtle Robot, play Knuckles as the leader (with a partner) and climb up the wall.
Unlock Knuckles, Cream and Amy
To unlock Knuckles, Cream and Amy you do not have to delete the game. You only have to defeat the Final Boss as either Sonic or Tails. Then revisit all of the Sunset Hill stages including the boss stage. For Amy complete all the stages for Toy Kindgom including the boss stage. And finally for Cream complete all the stages of Cyber Track including the boss stage. You do not have to have any Chaos Emeralds to do this.