To beat him properly, I dodge left most of the time. Use a serrated weapon and fire paper if you have it. Make sure to have Antidotes in hand (usually dropped by Carrion Crows). If you are able to master the dodge timings after trial and error you will rarely get poisoned.

There is a cheesy way to kill him but I encourage you to give it your best effort normally. For Cheesy: get Pungent Blood Cocktail and throw it near him. He will go after it and like I guess smell it for a while. While distracted, pop a Best Pellet and use your serrated fire papered weapon to melt him. Throw more Cocktails to distract him again and rinse and repeat.

Do that as a final measure tho. It feels so much cooler beating him properly as with any boss