Hints:

Allow a game to idle for over three hours to unlock the "Hints" option in the "Extra" menu.

Hint: Bosses

Play Sonic Gems Collection once every day and accumulate over 24 hours of game play. Then, start the game 30 to 70 times to unlock the different end bosses to Classic Sonic games that you can play.

Hint: Unlock full versions of game demos:

Once you have unlocked all the playable ending demos, go to Sonic The Hedgehog, Sonic 2, Sonic 3, Sonic 3D Blast, Sonic Spinball, Robotnik's Mean Bean Machine or Sonic Chaos. Keep intentionally killing Sonic until you are out of lives. The game will end, then restart at its own title screen. From there, you can start at level 1 of the game and play until the timer reaches zero.