did you beat him? if not then...

just focus on wearing down his stamina then attacking him when there's an opening. block/parry his normal attacks, get in a couple attacks of your own (these won't affect his health most likely, just his stamina), dodge when he enters one of the red unblockable attacks, then attack immediately afterwards (this is where you'll do damage). try to dodge in such a way that you're still close to him when he's finished with the red unblockable attack so you can quickly launch into a flurry of attacks. you'll only need to repeat this about 5-6 times to defeat him. good luck! i absolutely loved dathomir and thought this fight was a lot of fun, but i also had to play on easy mode cause i suck shit at combat.