If you are having a difficult time with this boss my first successful kill was with a gunslinger.
Before going for the boss it will help if you unlock Preferential Treatment in the soul shop which will allow you to lock in a gunslinger permanently in the character selection. I then did a full map clear of all regions and died and locked the map down after picking the gunslinger which allowed me to warp straight to the boss as much as I needed.
For the fight itself it's not "easy" but being able to freely hover while attacking even with an empty magazine made dodging a lot of the attacks much easier. You'll want to get comfortable in the air and stay mostly in the upper 3rd of the arena so you have plenty of space to spin jump off of the yellow orbs and the red skull attacks. Staying in this area will put you safely out of the explosive radius' of the eyes and you'll only ever need to land to refresh your double jumps.
I recommend reloading during and after spin jumping as you won't be able to shoot during this time and if you time it will you'll never have to land very often.
The other thing of note is during phase two you'll want to get a bit lower in the center of the stage when possible and drop your dynamite so that the cross pattern can hit the bottom eye and one of the side eyes. it's not a lot of damage but it helps. The dynamite can also be used to kill the red skull projectiles if you aren't in a spot to spin jump off of them or shoot them in time.
The most important thing to remember is if you have to shooting with an empty mag still keeps you hovering in the air but you will slowly start to decent. that extra bit of hang time is very valuable for weaving in between the blue shot volleys.