Successfully complete the game, then press L(2), R(2), Up, Down, Up, Down, Left(2), R(2), Right(2), Left, Up, Start when 'Press Start' appears at the title screen to unlock Diablo Tiger, Cyclops Type 1 and Cyclops Type 2. A sound will confirm correct code entry.
Gilvader and King Gojulas
Successfully complete the game, then press R(2), L(2), Down, Up, Down, Up, Right(2), L(2), Left(2), Right, Down, Start when 'Press Start' appears at the title screen to unlock Gilvader and King Gojulas. A sound will confirm correct code entry.