If O&S bring the most joy then BoC brings the most frustration. I went through about 4 Rings of Sacrifice before i finally defeated it. I tried to do it light and with the woodgrain ring but that wasnt working well so i went in as Tarkus and it worked better because i could block most of its attacks but then i'd get swept into the abyss.
I almost threw my controller on my last attempt. I made the jump to the middle which was my first attempt, next thing it does that Pyromancy attack and i swear i thought i died, but i probably had about 1-20 points of health left so i drank up and finally defeated it.
I'll go after Prissy, pinwheel skeletons were the only thing i didnt wanna encounter but i should be able to squash them with my Tarkus set.