Hey, come on guys, this game is way better than most of those tower defense games. In fact it deserves 3 more stars than they do. This one is worth a whole 2 stars!
Better yet, make the Hard badge earned for firing 10 nukes in one round (normally the max is 5, but...) That way it's hard, takes a long time, and not obvious.
Level 14's the worst. The trick to getting the last ninja before he can get to the gems is to build temples on the high ground near the entrances early enough to fully upgrade them (Burning, not radiating) by the end. Also have Dens as high level as possible overlapping the entrances as well. Then shift click the fully-upgraded meteor spell on him 5 times and he should go down. It was the only way I had a chance. Height advantage also helps.
 "One Shot"){kind=icon}
 "P.O.D."){kind=icon}
 "Particles"){kind=icon}
 "Gravitee Wars"){kind=icon}
 "Balloon in a Wasteland"){kind=icon}
 "Cursed Treasure: Don't Touch My Gems!"){kind=icon}
 "Infectonator : World Dominator"){kind=icon}
 "Tower of Greed"){kind=icon}