Press A,A,Up,B,B,Down,A,B,Start at the title screen. You'll have to pause the game once playing to beome invincible.
At the title screen, press A,A,Up,B,B,Down,A,B,B,Start.
At the title screen, press Left, Up,Right,Down,Up,Right,Left,Down, and then your "level button". Up (level 2), Left (level 3), Down (level 4), Right (level 5), Select (level 6), B (level 7).