Ending:

Press A, A, A, B, B, B, START at the title screen to see the ending.

 

Sound Test:

Press A, A, B, B, START at the title screen.

 

Various Cheat Codes:

At the title screen, press Start to go to the title menu. From there, you can press A and/or B varying numbers of times (per the below list) for various cheats. The order of the button presses (other than Start) does not matter, but the quantities do.
 

Effect                                                 Code

Level 2                                               Press A 6 times and press B 6 times, then Start.

Level 3                                               Press A 10 times and press B 9 times, then Start.

Level 4                                               Press A 13 times and press B 3 times, then Start.

View Extra Day 1 End Event             Press A 4 times and press B 4 times, then Start.

View Extra Day 2 End Event             Press A 6 times and press B 2 times, then Start.

View Extra Day 3 End Event             Press A 8 times and press B 2 times, then Start.