If you are talking about DH 2014, there are individual promotions that happen periodically. You have to enter a code when there is one active. There aren't any active at this time.
If you're not talking about DH 2014, I suggest asking in the forum of the game you are referring to. You can see the available forums in the Game Communities.
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If you're not talking about DH 2014, I suggest asking in the forum of the game you are referring to. You can see the available forums in the Game Communities.