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When playing with a friend online with my custom decks he cant play land what would cause this ? and how do we fix it ?

You guys are probably playing with two decks that the other doesn't have. Also, from my experience of playing with a friend, if you two have too many decks that you both dont share the game will lag even if you are playing with decks you both have. Go over with your friend and add/delete wads that you both don't have and make sure you have the latest updates of the modder's wads as they update them frequently.