At the main menu, press X, Y, B(2), Y, X, L(2), R(2), Up, Down, Left, Right, Start, Select. If you entered the code correctly, you will hear a sound.
To unlock Azrael and Huntress, you need to finish the entire game (all three chapters). After the game's ending credits, return to the batcave and both characters will be unlocked and made available to purchase.
To unlock Villain Hunt minigame, finish all Villain chapters with True Villain status for every story mode level. After completing all Villain chapters, Villain Hunt mode will be unlocked and accessible from the batcave computer.