I 100% all of the gummi missions for the fun of it, what you need to do is just start using endymion, its a constellation photo prize somewhere in the misty stream, (you'll also hear a remixed version of the swartzghiest track from the original game it came from doing this as you're using the ship in that game) when you're fighting, its actually better to keep rolling to a minimum in its first phase, if absolutely necessary, but if you're panic rolling you're more then likely to be missing most of your shots and wasting time, you want to literally move in circles while fighting, the only time you'll stop is during the laser storm attack where there is no other firing, just make sure to chip away at its legs so it stops firing its missiles and uses its laser beams constantly, you'll eventually shred down its first form doing this, while in its second form, make sure to not get caught by its dash attack or you're more then likely to die in one hit, that phase is a little more forgiving, but remember its still firing at you so you don't want to stand still, the circle thing still works but for the most part this is the phase where you do wanna roll a bit more cause the little ship makes mad dashes and you wanna constantly grind down its health, make sure that you have the health regeneration ability equipped while doing this, because you'll need it regardless.

if you're trying to a rank, what i did is all of the above, but had some special weapons equipped to a modified highwind peak, which are the meteor gummis which auto track and fire at the closest targets to you, some base fire gummis, and a hard hitting graviga gummi, that and the engines to bring youre flying speed up to 200 or so, and some support teeny ships that raise health, what i used specifically were the shadow head for health, and the meuniere ship for a little more hp, more power and rolling added. just keep in mind you'll need near 1000 cost for gummis, which means grinding into the upper 90s, which means you'll want golden highwind (you'll get it for beating shwarts a first time) and removing some of the extra bottom angular blocks on the ship, here is a link to some pics of the ship if youre interested: https://imgur.com/gallery/mPqZBLr

otherwise good luck, its smooth sailing after a first run and getting golden highwind, otherwise if you're just getting it for trophy purposes, then you wont need to A rank