Press L1, R1, R2, L2, Select, Start at the title screen to unlock Bubble Bobble, Cameltry, Kiki Kaikai, Metal Black, and Syvalion.
Bubble Bobble
Play all default games at least one time.
Cameltry
Accumulate at least one hour of game play in Lunar Rescue, Ah Eikou no Koshien, Alpine Ski, Cleopatra Fortune, Puchi Carat, and Flipull.
Kiki Kaikai
Accumulate a total of five hours game play.
Metal Black
Accumulate at least one hour of game play in Space Invaders Color, Space Invaders DX, Darius Gaiden, Grid Seeker, and Majestic Twelve.
Syvalion
Accumulate at least one hour of game play in Elevator Action Returns, Kuri Kinton, Jigoku Meguri, Don Doko Don, Rastan Saga, Fairyland Story, Pulirula, Lightbringer, and Runark.
All hidden games...