On level 12, no matter what I do, what towers I build where, etc, the very last champion (big ninja) ALWAYS manages to grab the first gem before he gets killed. I can't find any way to prevent it whatsoever...
Tutorial:
Start a new game. If you started in Madagascar, play. If you didn't, either start a new game over and over until you do, or find a game not coded by a retard that actually works.