I had one of those moments where you just had to step away and take a break from the game. Logarius, the boss of Forsaken Castle Cainhurst, is one of those bosses that is easy to understand, but difficult to execute on. The main frustration for me was getting him to a point where I could actually get in melee range. I think I've figured that part out - just being super-aggressive in phase two, making use of the interruption your melee attacks inflict on a lot of his spells and just getting the hell out of there when he summons a big red skull of doom.
I actually got him down to about 10% in one run, which was not coincidentally the attempt when I managed to interrupt his buff that he casts on himself in phase 2. Logarius has been going to walls a lot lately, making it impossible for me to get behind him to the narrow enough degree that my charged R2 will stun him. Anyway, maybe tomorrow I'll come at it feeling fresh and ready. For now, though, I'll have to farm some blood vials. My Hemwick route still provides a decent number of echoes, but I'm getting to a point in leveling where it's not really providing enough to bump up anymore. Luckily, though, I can wail on the executioners, no interrupt needed, and take them down in three hits, so it goes faster and more reliably (and saves me bullets, which I also need to farm.)
But lest the day seem bereft of progress, I've beaten Rom the Vacuous Spider. The real key that I discovered was simply not locking on to the little spiders and making sure I could always see what Rom was doing. Mostly I would draw the spiders out so that the upward-comets and arcane aoe were never a threat, and I'd just look out for when she started perking up to make sure that I could run from the standard comets.
Additionally, i used some bolt paper, which increased my damage significantly. Obviously, I saved this for once the spiders were cleared so that I could ensure that I was using as much of its duration as possible on the boss itself.
So in addition to the DLC area (which I'm going to hold off on for a bit) I've got Yahar'gul (the extra-creepy portion) as well as Nightmare Frontier. I suspect that a little longer working on Logarius will see him down, and then I'll probably get and upgrade the Logarius Wheel. I figure by the time I have to choose which weapon goes to +10 I'll have the Whirligig Saw and plenty of chunks to get a couple of +9s.