Ashen Idols, Giant Club Demons and Possessed Armour all try and block your path to this boss battle.
Head to the foyer bonfire in Blume Tower and use the lift to the area below. On the far side is another lift which you should take to a lower level but as it moves turn around to see two paths. Run and jump as the lift passes the uppermost path. In the room ahead you’ll find a Strength Ring in a chest. Use ranged attacks to take down the enemies you can see through the hole in the floor.
Drop down into that room and again kill as many enemies as you can through the holes in the floor before dropping down again. Look out for the two Axe Demons with flaming axes.
When you drop to the fourth and fifth floors there’s a damaged area on the floor in a corner. Step on it and you’ll fall through multiple floors, as will any enemy that treads on it. You’ll find a Partizan +6 weapon on the sixth floor just below the bottom floor, and from the floor with the weapon, you can see three enemies below.
Take them out from the safety or your room above and then drop down but expect a little bit of damage from the drop. On the bottom floor pull the lever and open the large door and run past all four enemies as you can’t kill the Possessed Armour until the Ashen Idol is dealt with.
Before the stairs is a path on the right that goes to a chest and a Sorcery Clutch Ring but leave it until you’ve disabled the Ashen Armour and killed the enemies. Go up the stairs in the room ahead and down in the lift to the level below.
Step off and it will go back up to the top. Go up the stairs in front of you, and you’ll see four Ashen Idols. Again, you can’t kill the Giant club Demon here until at least two of the idols have been dealt with. Once you’ve disabled the Ashen Idols and killed the enemies, it’s time to enter the mist for a boss battle with the Fume Knight.