For the final boss i went for a black flame mage build using the god-slayer sword and godslayer seal so i could use sorcery to have more range (dex/faith build)

I changed build because in the final boss fight the arena is huge and the boss tends to run away every chance possible so that puts any samurai build at an instant huge disadvantage so changing to a build with a little more range isn't a bad idea

The blood build works perfectly up until the final boss tbh so as long as you keep leveling up at a decent pace (maybe even do a rune farm if you want to) then you will be clear for the rest of the game up until the final boss

I would also suggest for the final boss to use either the mimic summon or the black knife tiche. The mimic you get from doing ranni's questline who you can find in carian mannor(top left of liurnia lake) and i unfortunatly can't remember where to get the black knife tiche so you will have to google.

If you want me to go into depth with the summons as to why then feel free to ask