Codes
Press the control pad left or right to reach the different letters. if the password is enter correctly you will hear a tone then it will take you back to the main menu
Enter the following to get the following monsters

Purple Alien-B1G4L
Ralph-LVPVS
Lizzie-S4VRS
George-SM14N

Cheat Menu
First, go to the password screen. Then, Enter in 'BVGGY'. You will have the cheat menu!

All Characters
To unlock all characters, type GOT3T at the password screen.

Play as Myukus
At the password screen type in N0T3T. In the code there is a zero and not the letter O.

Play as Nubus
Enter the following password to play as Nubus: SRY3D.