Secret: When a friendly minion dies, put 2 copies of it into your hand.
The one time when duping cards won't get your account banned!
Secret - Hidden until a specific action occurs on your opponent's turn.
How to Unlock Duplicate
Unlocked in The Plague Quarter, in the Naxxramas adventure.
How to Unlock Golden Duplicate
Crafting unlocked in The Plague Quarter, in the Naxxramas adventure.