Unlockables: Gotta unlock 'em all.
Go to Professor Rowan's lab after you complete the Sinnoh Pokedex. Professor Oak will then give you the National Dex.
Blue Trainer Card (One Star):
Beat the Elite Four
Bronze Trainer Card (Two Stars):
Win all of the Master Rank Contests
Silver Trainer Card (Three Stars):
Complete the Underground Flag minigame
Gold Trainer Card (Four Stars):
Capture 482 different Pokemon
Black Trainer Card (Five Stars):
Win 100 times in a row at the Battle Tower