I'm on my second play through of Epic Yarn trying not to lose any beads and I just defeated the last boss.
WARNING: DO NOT READ ON IF YOU HAVEN'T COMPLETED THE GAME!!!
It is actually quite hard not to lose ANY espicially on the bit after Yin summons the dragon and he starts firing rockets and you've got to jump on the yellow thread. It takes me ages to get through.
My favourite bit was when Kirby turns into a tank and they compete in a firing match. Epic!

I still think the Meta Knight fight was harder.
What were you guys experiences with the last boss?