As you enter the dungeon and head towards the very first site of grace, make sure to loot the nearby chest and grab the Rune Arc from it. From there, the path forward is very linear and there isn’t much to pick up or see. Your only company will be a couple of hungry rats until you continue far enough to find a tunnel with a weak floor that will crumble under your weight.
This time, you want to fall through to the lower level as that’s the only way forward. Doing so will allow you to reach the lower level where you will find a bunch of exploding undead behind bars.
As you proceed further through the dungeon, be careful while approaching the locked wooden door as a sneaky enemy will jump down to try and ambush you. Continue past this door and you will reach a small ledge that you have to jump down from. As you jump down, you will be forced to fight 2 more enemies trying to ambush you, with the first one standing to the right and the second one right below you as you jump down.
Now that they’re dealt with, continue going through the next hallway and you will reach a room with a locked gate to the left (A) and another set of tunnels to the right (B). While the gate to the left is locked, there are two enemies keeping watch next to it. Killing them will ensure that you do not get a nasty surprise by going straight to the right.
As you go through the set of tunnels to the right, when you reach a turn you will need to watch out for the pack of rats hiding to the left. And if you thought you were finally going to get some loot, all they’re guarding is 2x Turtle Neck Meat. But don’t worry, once you reach the next room you’ll start getting some well deserved items.
When you reach the room with a visible chest and bookshelves, don’t rush in as there is a pretty rough ambush ahead. On top of the enemy in front of you, there is another to the left of the door, as well as one to two more enemies on the second floor.
To deal with those enemies, come close enough to trigger the ambush before running away from the room. This way, the enemies on the ground floor will follow you first and you’ll be able to dispose of them without getting attacked by the ones on the second floor. Once the way is clear, grab the Somber Smithing Stone  from the chest as well as the Golden Rune  from the corpse on the ground floor, and proceed up the stairs to find a lever that allows you to not only open the path to the boss, but also the cells that were previously closed.
While the cells are now open, backtracking towards the dungeon’s entrance will only yield a Golden Rune . However if you jump out of the room, you can find the Pillory Shield in a nearby cell.
With the path forward now open, start heading back to the gate that was guarded by 2 enemies. In the hallway leading to the room with the now unlocked gate, grab the Wakizashi, the Stonesword Key and the Golden Rune  from the cell to the left before going forward.
Once you reach the room that had 2 enemies guarding it until you murdered them in cold blood before unlocking the cells, loot both corpses for a Golden Rune  and a Rainbow Stone before breaking the wooden planks to the southwest.
Behind those planks, you will find a set of platforms that allow you to get all the way down. As soon as you reach the bottom, the Frenzied Duelist boss fight will begin.