All cards
Beat every duelist 20 times, then at the title screen press L, R, Select, A, B, Left, Right, Up, Down, Start

Faster Duel Speed
When choosing a duelist, hold down L until the duel starts. The gameplay speed will be twice as fast.

View the staff credits again.
To do this, you must have already viewed the staff credits at least once. To view the credits again, press Up, Up, Down, Down, Left, Right, Left, Right, B, A at the selection menu.

Unlock the Limitation option
To unlock the limitation option, get 100% completion by collecting every single card in the game. Now you can choose to have restricted cards to be no longer restricted