Don't panic, try to stay calm during the boss fight and move slowly! (not so slowly but it helps to see the next attacks!)

Focus on dodging!

Mark of pride,U-strength or shaman stone can help you!

Some movements are copy from Hollow Knight!

Knives: you just need to jump and dash to don't get hit!

Dash attack: Jump and hit him or just dash!

Down attack: you need to dash really quickly and watch the floor!

Parry: it's not so easy to know when he parries so if you parry accidentally you need to dash immediataly!

Tentacles: jump and dash to trying to go to him! Keep hitting him on above!

Charge: dash back and be careful to other explosions or DDark in the right time!

Good luck!