It seems that also Dragon Spirit has a few hidden easter eggs built-in, such as a sound test which can be activated by holding A, B, UP on controller 2 and then pressing the reset button.
Then you'll be taken to a sound test screen where you'll be able to listen to all the great music within this game. The tunes are selected by using controller 1.
If you feel like cheating a little then, while being on the sound test screen, you press B, UP, UP, B, DOWN, DOWN, B on controller 2 for a level select. Use LEFT or RIGHT on the D-Pad on controller 2
to select the level you want to play, Then press START on controller 1 to play the level.
If you'd like to start the game with 20 dragons instead of just 3, then intentionally loose the prologue and then hold A + B and press START at the titlescreen.