Invincibility and Power-ups
At the title screen, press A, A, Up, B, B, Down, A, B, Start. While playing,
pause the game and immediately resume for invincibility and full power-ups.
Level Select
At the Credits screen, press Left, Up, Right, Down, Up, Right, Left, Down
followed by one of the following:
Level  Button
2      Up
3      Left
4      Down
5      Right
6      Select
7      B
View Ending
On the "Press Start" screen, press A, A, Up, B, B, Down, A, B, B, 
Start.