I am getting my son the two player battlebox starter for his birthday and I have a question. If I want to buy him an additional booster or two...should I go for certain sets/series that are compatible with this base set or will pretty much any of them work? What about the building expansions? Just curious what will make his birthday that much better in addition to the base game.
Also, what is the overall health of the franchise? Selling well...or in decline?