To become a Ninja in Club Penguin you have to get a black belt in the Card-Jitsu game. To do that you have to keep playing the game and win!
To get the first few belts you have to win a certain number of games before Sensei will award you the next one:

And you will be able to buy things from the Martial Artworks Catalog (the Ninja catalog).
Here is the Martial Artworks Catalog (the Ninja catalog):
Hey!! Once you earned the amazing black belt and defeat the Sensei, you can enter the Ninja Hideout!!

You can then buy lots of Ninja stuffs, like Ninja Clothing and Ninja Furniture in the Ninja Catalog!! Below are pictures of all the Ninja items in the Ninja Catalog!!








White belt = 3 wins
Yellow belt = 5 wins
Orange belt = 7 wins
Green belt = 9 wins
Blue belt = 11 wins
Red belt = 13 wins
Purple Belt = 15 wins
Brown belt = 16 wins
Black belt = 17 wins
When you have your black belt you have to play against Sensei (click on him and then choose Sensei Mode) – it takes seven goes (keep trying if it did not work, he gets weaker as you go along) but when you beat him he will give you a special face mask and you will have access to the secret Ninja Room where you can play against other Ninjas.

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Hey, I read a lot of blogs on a daily basis and for the most part, people lack substance but, I just wanted to make a quick comment to say GREAT blog!…..I”ll be checking in on a regularly now….Keep up the good work!
woaw