Godzilla Generations Codes -

Play as original Godzilla:
Hold L + R and press any button at the monster selection screen. Alternatively, successfully complete the game once.

Play as Mecha Godzilla:
Hold L + R and press any two buttons simultaneously at the monster selection screen.

Play as Beta Godzilla:
Hold L + R and press any three buttons simultaneously at the monster selection screen.

Play as American Godzilla:
Hold L + R and press any button four times at the monster selection screen. Alternatively, successfully complete the game as the original Godzilla.

Play as Minilla:
Successfully complete the game as American Godzilla.

Play as Dr. Serizawa:
Successfully complete the game as Minilla.

All VMU monsters:
Enter the "VS Battle" menu and select the bottom option on that screen. On the next screen, hold X + Y and press Down + L + R to unlock up to forty-four monsters. Note: Only less than ten monsters will appear in the VMU.

Hint: Regain energy:
Press Y when in a safe location as Mecha Godzilla to regain a small amount of energy.