At the Monster Selection Screen, hold L and R and press any button three times.
Unlock Beta Godzilla
At the Monster Selection Screen, hold L and R and press any button six times.
Unlock Dr. Serizawa
At the Monster Selection Screen, hold L and R and press any button two times.
Unlock Mech Godzilla
At the Monster Selection Screen, hold L and R and press any button five times
Unlock Minilla
At the Monster Selection Screen, hold L and R and press any button.
Unlock the First Godzilla
At the Monster Selection Screen, hold L and R and press any button four times.
Unlock the United States Godzilla