Extra Mode
Upon completing the arcade mode and the credits, you'll be informed that you've unlocked Extra Mode. When you start a new game and choose Arcade, you'll now be given the option between playing Normal and Extra Modes.
Extra Mode: Beat Arcade Mode on any difficulty.
Stage Mode
Complete the first stage to unlock stage mode. Allows you to replay already played stages.
Stage Mode: Complete the first stage.
Endless Mode
Complete all stages in Arcade Mode to unlock Endless Mode, where you can: Play each stage successively without boss battles.