I see a lot of questions about the spin attacks so i'm gonna try to explain it in depth. i may make videos if people are still having trouble
Air spin: the way i got this was at the end. when the armor is completely gone, jump once and start hitting A. the spin attack should start and if you kill the boss and the screen goes white keep hitting A and you should get it no problem. but if you want to try to get it any other time in the game jump once because the spin attack stops once you get above the boss so start as low as possible.
Ground spin: i recommend doing this when he is either stunned or the armor is gone. just stand in the middle and repeatedly hit A. it's not as obvious as the air spin attack because he is just rotating in the ground one. if he doesn't do it try pressing right to start it sooner.