When you get all the giant coin things go to the mushroom place where you can buy new backrounds(it's above the first levil after you defete the last boss)and where there was an out line there will be a new backround (you might have to buy all the mushroom houses first) it will cost 20 big coin things thats the last amount if you buy all the mushroom houses and collected all the big coins. buy it then when you go out wher the number of how many big coins you have normally is it will say all spent