To defeat the invisible ninja, you need to be lucky of freeze or scare them with the first tower. To get brilliant at the harder levels, I'm just using the chilling crypts because of that. Unbalanced game.
Too many bugs. The robots don't do the same than you did before so many times. But the idea of the game is amazing! Fix the bugs and that one is 5/5 score! At this moment 3/5...