This is how u do it! Beating the sensei:
1. Go to the Dojo Courtyard. Then go into the Dojo. You will see a green pillow. Put your cursor over it and click there. There is the Sensei. You will need to learn how to play and recieve your cards.
2. Play the Competition Mode. This is the fastest way to earn belts.
3. Beat the Penguins you compete with. If you lose, don’t get upset. Also, don’t close out if you are losing badly. It’ll just give you a bad reputation.
4. Keep winning Soon, you will earn the Black belt.
5. Play on sensei mode. This is the only way you can become a Ninja.
6. The Sensei will win the first 5-10 times, but don’t stop and he will weaken. He then does mistakes so,You will win! You will also be able to go to the ninja’s secret hideout at the stone thing in the left at the dojo courtyard.
Hope this helped :D