Select Level:
Enter the level selection screen and press C-Up, C-Right, C-Down, C-Left, R, L, Z, C-Up, C-Right, C-Down, C-Left. When you have entered the right code it will be comfirmed with a sound.

Get all weapons:
Enter the level selection screen and press C-Left, C-Down, C-Right, C-Up, Z, L, R, C-Left, C-Down, C-Right, C-Up. When you have entered the right code it will be comfirmed with a sound.