I found Abyss Watchers to be shockingly simple. Beat him on my 2nd try. The adds really help, because they'll attack the main boss too. The hardest bosses I think is Pontiff and The Twins. If you don't kill the mage brother early during the 2nd phase, the battle can really drag on. Nameless King was an epic battle that did take me more tries than I would like to admit, but I really only ever died to a bad roll and not the boss face rushing me like Twins, so I found him to be a little easier. Long story short, **** the twins, only boss I had to summon someone to help with.