This boss has about 8 attack types, and always chooses 2 to fire in quick succession. Some combos aren't bad at all, due to targeting the same area or having generous timing.
But then there's one attack that has always been difficult for me. It's a pair of canister grenades which airburst into a MIRV rain of overlapping parabolic projectiles which land at different rates. It nearly forces you to stay on the ground, or barely jump.
I got that attack 3 times in a row, combined with the orthogonal rockets (require careful jumping) and the purple orthogonal spur-field. Basically the three attacks I have the most trouble with, heh.
(I was so close, too, one hit away from winning...)
I did succeed a couple attempts later, and I'm not even mad. I really love this fight. It was a lot easier years ago though when it was laggy for me
Whereas I got through Asha on my first try, albeit with 1 HP left.
Ultimortal difficulty, though I didn't maximum charge, because I *really* cannot handle the Skysmashers.
Even the creator complains about them a little in his video:
https://www.youtube.com/watch?v=67eLpLhxEPg(at 30 seconds the boss starts spamming that airburst grenade I was complaining about)
Oh oh also, it's actually a feature that if the boss hits with an attack, it prioritizes that attack going forward.
Iji on Ultimortal. Jeez, 8 year old game... Recent update is really nice, though, adding 8 nonlethal weapons and other things!