Challenges are way to easy. All you need is 20 black cards for the first 7, and add a few contamination for the last.
Missions were a little more fun, but all in all just another card game.
too easy, there is a bug when you can get the curser off the screen and no star can hit you. Just happened to start like that for me 2000+ and counting.
There is only one city that is remotely challenging, well more like annoying. Nagoya with all their shogun ghosts that can 1 hit your hero if your wearing armour. other than that its too easy on normal difficulty.
 "Zilch"){kind=icon}
 "Mytheria"){kind=icon}
 "Kongregate Chat"){kind=icon}
 "Feudalism"){kind=icon}
 "Feudalism II"){kind=icon}
 "Bloons Tower Defense 3"){kind=icon}
 "Orbs"){kind=icon}