Originally Posted by Helg0r
the very last boss indeed has a pattern but it is a little bit vague. Observe the yellow balls closely and you will see that most of the time their trajectories stay roughly the same. What's random is their spin (clockwise/counter-clockwise), so basically you have to find a position where you can react to both cases. Keep at it!
I'll give it a shot - I didn't mean the last boss was random - just meant you can't really tell where the yellow balls are going - and the random spin is a pain at times.
After I avoid the first ball, I try to move laterally in the big space between the beads at the bottom of the screen. I've got it by loading a save, so I assume I'll get it eventually if I keep at it. The 25-30 min per try is just a bit of a pain.
BTW: How did you get it? Did you grind it until you get it, or play it casually a few times a week?
: I didn't realize you got it so fast... Do you have an idea of how many times you tried before you got the achievement?