So I bought Dark Uprising and got the weird double sided play mat thing. What the hell is it even for? In the rule book where you set up the game it talks about the tiles from the other game and then the 12"x12" tiles that you can buy (If you're lucky). It suggests making a 4X4 board out of the tiles and with now introduction scenarios, what exactly is the play mat you get with the game to be used for?