CheatOgre.com: Super Monkey Ball 2

Extra Levels
Beat all 10 levels in World 1 without using any continues on Beginner difficulty to unlock 10 more Beginner levels. Beat all 30 levels in Worlds 2 through 4 without using any continues on Advanced difficulty to unlock 10 more Advanced levels. Beat all 50 levels in Worlds 5 through 10 without using any continues on Expert difficulty to unlock 10 more Expert levels.

Master Difficulty Setting
Beat the 10 extra Expert levels without using any continues to unlock Master difficulty.