His favorite Pokemon is Mega Charizard-X, and I got him a M Charizard-EX (X) for his birthday. I'll ask him if he has any other favorite Pokemon or if he has a favorite type.
EDIT: Okay, he said another favorite of his is Kyurem. Other than the Boundaries Crossed decks with Black and White Kyurem, none come with Kyurem, do they? Also, he said he has a Yveltal-EX, so I figure Dark Hammer would be a good choice for him since Yveltal would fit right in.