This fight is really just a matter of making silly mistakes that are entirely on you as the player. Clearing the fight is one thing, then you also clear fast and perfectly it for the ability to purchase Friar Rush. Naturally you will get ahead of your self. For the normal clear, take your time and be patient. Make sure you are keeping your MP up because the longer you drag out the fight the more it’s going to cost you. When you clear it and are ready to speed clear, just damage normally until Gogo is in a phase that you can full in blow everything on him with Moonflute.

My heart actually almost skipped a beat when I got the achievement clear because after blowing all my skills and being pacified by Waning Nocturne at no more MP, Gogo was at .01 health. But part of my combo was Nightbloom and I realized the DoT tick would kill him. Sweet victory.

Gear up, learn the dance, perfect it. Literally every piece of content is like this.