Got to play a little last night which turned into 3 deaths in Quelaag's Domain (only two to the boss, oops).
Just a pretty basic question regarding my future strategy, both attempts I got Quelaag to half health.  Avoiding the lava pools and the area effect attack my downfall.  I tried the battle once with Gold Pine Resin, which was beneficial.  But I only had one batch in my inventory and I really shouldn't have used it on my first boss attempt.  I have a few doses of poison resin available, but is it worth using?  I tried to answer the question with a Wiki guide, but it lists things like poison or bleed resistance with an "A" "B" "C" "D" "E" or "S" and I don't know what those letters mean.  What means an enemy is highly resistant and what means highly susceptible?
Oh, and the dudes with the boulders are supposed to respawn?  First time I went through I killed them all, they all kind of dissolved away into white light like a boss, miniboss, or the blowdart guys.  I assumed then they would not respawn, but they actually do?