By complete the game the first time (world 8) you'll unlock Sound Test, Gachapon, and Boss mode. All three can be found in the menu by pressing R in the stage select screen. You'll also unlock World 9 which explains Stapy's part in the story.
#. Unlockable: - How to Unlock:
1. Boss Mode - Complete the Game
2. Gachapon - Complete the Game
3. Sound Test - Complete the Game
4. World 10 - To unlock World 10 you must complete boss mode at least once. World 10 consist of a series of time attack levels including a new boss.
5. World 9 - Complete the Game