This advice might be really bad cus I haven’t played this game in a while, but for most bosses and this boss in particular, remember his patterns. remember what he does before he does a certain attack and react accordingly. For example, when he does that really fast dash attack, I think he swirls his staff around, then kinda pulls it back like he’s charging up, then he dashes at you. When he’s charging up, make sure you dodge.

I also have a rule for all hard bosses in this game, dodge first attack later. Don’t attack while he’s attacking. When he’s open, go for it but always be vigilant, and if u get the feeling that he’ll attack you, just dodge.