I remember Orphan of Kos and Isshin taking a long time for me. Multiple days of several-hour long sessions, I assume. I would probably have trouble beating Orphan today too, but Isshin has gotten pretty easy for me over my 4 or so playthroughs. Laxasia from Lies of P is also a huuge pain despite my four playthroughs. I feel like her second phase is just waaay too much whereas her first phase has gotten pretty easy by now.
Currently playing Khazan and some of the bosses did give me a lot of trouble too. Especially the first two you get to after beating the tutorial were a pain because the bosses felt really spongy, I didn’t have a lot of damage, and they dealt damage like a semi-truck. I’ve gotten better at the game, though, and now bosses don’t take nearly as long. I’ve gotten better gear by now, I’ve got better skills to use, and my overall skill in the game is also good enough to not struggle as much anymore.
Which ones did give you trouble on your playthroughs?
I freaked out on sir Alonne runback and killed every mob 12 times until they disappeared. Then killed Alonne in the very next try
I caused extinction events on a couple different boss run-ups, I remember doing this for blue smelter demon as well. It is both practical and therapeutic.