Completing the boss battles without getting hit can be tough, i know it took me a lot of practise and patience. The thing which makes this boss battle harder in particular are 2 things
Instead of normal enemies you are facing wavy coloured tentacle things in yellow, blue and red. After playing the whole game against men, the appearance can affect your timing as you might not know exactly when there striking properly. Also the +500 points bonus on normal enemies? That's gone, now it's a purple ball which hurts you if you don't double tap it correctly as you normally would.
Apart from that, it's business as usual. You need to basically hit everything in this song as the purple double tap 'bonus' hurts you as well, so you can even slip up there. This will take practise, but in time this will start to get easier.
A couple of moments were constantly throwing me off, when you have the sets of double red coming at you constantly with yellow in between and some of them had to be double tapped (Which hurts you know if you miss)
Of course this goes without saying but playing on Expert is easier than Master. Good luck