Step 1: On the main menu screen, select the first icon (it looks like a gear).
Step 2: Select "Redeem Code" (looks like a white computer).
Step 3: Type in the code. Press "Enter" It will be in your Deck Builder.

Code	Effect
123224	Unlock Music Mallard
BRIEF	Brief Power
C3R3BL	Cerebral Blood Storm
COOLDUDE	Gets freezy j.
CUTIE PIE	Unlock Snuggle Tree
DRKUNGFU	Doctor Finn Character
MINSTR3L	Unlock Embarrassing Bard
P1GGY1	Pig
WINTER BMO	Unlock Winter BMO