Once you have collected all of the cards in a deck, you have mastered the deck. This means you cannot trade away any of these cards (except for doubles, of course) but you will receive some rewards for doing so.

Card Deck MasteredRewards
Regular Deck2 regular card(s) of choice, 3 random regular cards, and 1 random special card
Special Deck2 special card(s) of choice, 2 random regular cards, and 4 random special cards

Chain Mastering

For every 5 decks you master, you will recieve a prize pack of 1 choice card, 10 random cards, and 10 Points!