Very good and impossible mode game and in the game it well be hard to defend and cool game it's like one of the minecraft guns and like a zombie war app but it's easy that they say they want you to kill zombies but the hard and impossible part is defending your fortress rule one: call in airsritke to make it easier to defend.rule two: kill group zombies and purple zombies in area and that's what I was doing with rocket lanchers and machine guns. It's much awesome too!