just keep playing him if you have your black belt, he will eventually let you win.
You do the same in card-jitsu fire
because he is a card jitsu master
after you defeat sensei you get your ninja mask. you are then free to explore the ninja hideout or if you are a member play card jitsu fire
Do you mean card jitsu cards? Well most Asda's MABYE Morrisons and probablly your local news agents.
Beating sensei is really hard, you have to be fast. I suggest putting your computer in low resolution mode.