Okay, i’m gonna name one that might raise some eyebrow.
Halflight, Spear of the Church from Dark Souls 3 Ringed City. I know i know, but i can explain. I’m doing a knife only, no summon run, i mainly use Brigand Twindagger for everything, and occasionally Bandit’s Knife for anything susceptible to bleed, and it’s quite a good run, beating anything with varying difficulty, and even Demon Prince were defeated with a knife, then comes Halflight, Weeb of the Church. Technically it isn’t a hard one because it’s basically vs an npc invader, but the difficult came from the constantly spawning Guardian that’s also do healing and also using a knife, and also the long reaching and parrying weeb sword of Halflight. I couldn’t get past this one no matter how much i try, it’s the most difficult “easy” fight i’ve ever did on this run, where the second most difficult one is…Deacon of the Deep.
There’s a lift right at the side of the main entrance into the bossfight arena that cut down the runback time. You can just rest at the dragonslayer armour and then take the lift up right to the entrance, skipping the annoying stairs of enemies.