To enter a password for a card, press R3 at the "Build Deck" screen, and enter an eight digit password:

Card - Password

Ancient Tree of Enlightenment - EKJHQ109
Aqua Dragon - JXCB6FU7
Beast King of the Swamp - QXNTQPAX
Birdface - N54T4TY5
Black Hole - UMJ10MQB
Blast Sphere - CZN5GD2X
Change of Heart - SBYDQM8B
Crush Card - SRA7L5YR
Dragonseeker - 81EZCH8B
Earthshaker - Y34PN1SV
Elf's Light - E5G3NRAD
Fairy King Trusdale - YF07QVEZ
Fairy's Gift - NVE7A3EZ
Gravity Bind - 0HNFG9WX
Greenkappa - YBJMCD6Z
Harpy's Feather Duster - 8HJHQPNP
Horn of the Unicorn - S14FGKQ1
Magician of Faith - GME1S3UM
Doppleganger(Mimicat) - 69YDQM85
Mystical Capture Chains - N1NDJMQ3
Barrel Dragon - GTJXSBJ7
Robotic Knight - S5S7NKNH
Royal Decree - 8TETQHE1
Left Arm of the Forbidden One - A5CF6HSH
Seiyaryu - 2H4D85J7
Serpentine Princess - UMQ3WZUZ