All Quests
To unlock all Quests enter the following combination at the Quest selection screen:
L+R, Down, Up, Click the Left Analog-stick, White, Up, Right, Left, Down, L+R
If you entered the code correctly you will hear a confirmation sound.

Bonus Level
To unlock Bonus level enter the following combination at the Arena selection screen:
L+R, Left, Up, X, Up, Right, Y, L+R

All Duelists
To unlock all Duelists enter the following combination at the Character
selection screen:
L+R, Down, Up, X, White, Up, X, Black, Up, X, L+R