To become a ninja on the video game Club Penguin, you must beat the Sensei. There are several steps you must go through to do this, including going to the Dojo and clicking on the pillow that will take you to play a game of Card-Jitsu. You can find more information here: http://teamclubpenguincheats.blogspot.com/2008/11/how-to-become-club-penguin-ninja.html
