focus and memorize attacks

Utilize short dashes and short flight. In most cases you die very similar to how you die in souls-like games: not managing movement then running out of stamina. High DPS builds are the way to go, kill them before they can touch you.

If you're playing with controller, I'd recommend switching to keyboard and mouse instead. Using the mouse, in my experience, makes aiming with your attacks much easier. On top of this, you can much more easily execute short dashes as Spaghetti Meatballs mentioned since the dash is bound to your right click! (Also left shift, but I never used that keybind.)

Learn how long you need to dash, sometimes flight is a better option than being on the ground. it is tough though

so like sometimes a SHORT dash would be best, itll refill your stamina bar faster because you dashed less/end it early. as i said, sometimes.

variety of weapons helps a lot too. some that explode or deal aoe are GREAT for handling summons that some bosses use while the single attack versions (like furthest is laser) seem best for dpsing the boss itself.

overall just finding your own flor helps a lot, theres also people who post their no hit runs, and even pacifist runs if you desire to look up some of it as a guide or such.

Dont give upo!!!

try learning the boss, if ur having too much issues with certain phase, just train it outside fight in "Practice" menu. It will just take less time to reach it. Also dash sometimes can be extremely annoying to aim propely due to how rng it can be. And it's telling u a player, that 100% all of the game (except pacifist no hit). Just find strategy that makes phase as consistent as possible and excecute it multiple times so u can remember what to do when u reach it. It's mostly and about skill and a little bit of rng.

Ice Grenade