It is not with "a" rank buddy, with "A" rank buddy. So you have to select a buddy with "A" rank or class to play secret mode with. Buddy has rank like "A", "B", "S", "SS".
Good luck!
Comment found on LINE Bubble 2: Top
How to play secret mode one time with a rank buddy?
Comment found on LINE Bubble 2: Top
How do you get 17 30 combo in 1 secret mode? I just have that one left & 14 is the most I can get.
Comment found on LINE Bubble 2: Spongebob bingo
How to get lots of points like million on secret mode, it's unbelievable but many people did it!
Comment found on LINE Bubble 2: 245