When I first encountered the sewer beast i got extreamly fustrated and threw a open soda bottle at my computer monitor, and then i took a minute to find the most pain stakeningly grindiest way to kill him so that is exactly what I did before you start u will need a few things.
What You Need Before Fight
- Long Surgical Knife with atleast +5 blood absorption.
- Claw ability.
- Perferable Cuagulate ability.
What to Do During Fight
So what you do is simple you wait for him to attack, dodge, attack with surgical knife make sure u hit 2 times, then hit 4 times then use claw once.
Repeat that process and when ever u are low on health those 2 times u saved, are for Apothcary to heal ur self this will not work the first try you will have to do this over and over until u get it right, BUT this is the best method i had found of deafeating this darn sewer beast.