Card Minigame
When in the snow mobile, hold X and press O repeatedly (About 10 times) until a small card game appears where you match images. Match them quickly enough, with few errors, and you can win great prizes.
Completion bonus
Successfully complete the game to unlock the "Art", "Bestiary", "Music Player", and "Soul of Rebirth" options.
Seals
Northwest Seal: Break four seals. The fifth one will be the Boss.
Northeast Seal: Break eight seals. The ninth one will be the Boss.
South Seal: Break twelve seals. The thirteenth one will be the Boss.
Unlock Extras
Art Gallery allows you to view game art that you have unlocked. Bestiary give you information on monsters that you have defeated. Music Player allows you to play any BGM from the game. Soul of Rebirth adds additional gameplay. You have to beat the game once to unlock them.