I think most of my fun for this game was zapped out of it with having to farm for blood vials, antidotes and molotovs for blood starved beast. I bought the key to go further and kind of did that a bit, but I just have this shitty nagging feeling that I'm going to be bummed about more shitty farming like that. I really just hate that system. It's not challenging, and it's not because it's hard that I want to quit. I really want to try and fight the boss again and figure things out, but not like this.
Here is a protip: you can farm for vials while practicing against the boss.
Ring your bell in front of the boss' door and try to help the host without using vials or antidote.
Not only you'll get better against the boss but also you'll be rewarded with echoes and items (on your way to the boss).
You reallly don't need antidote or molotov to beat it.
That boss used to be a nightmare for me. But I got to the point where I can beat it without using vials/antidote/molotov/whatever. The only thing I use now is the flame paper, but it's not required either.
BTW, the Saw Cleaver is very effective against him, so you may consider using it if you didn't already.
Good luck!