Steady Hand McDuff is found in The Lost Bastille, behind a wall that can be destroyed with the use of an explosive barrel at the top of a staircase next to a Undead Jailer. You can also unlock the workshop by using the Lost Bastille Key.
McDuff needs the Dull Ember to begin customizing weapons and armor along specific upgrade paths using stones which can make unique weapons. He also becomes a vendor, selling minor equipment and upgrade resources.
Royal Kite Shield
Health and SoulsEdit
McDuff is losing his mind, evident by the swinging of his hammer at nothing except open air, and murmurs about a soft, fading ember, revealed to be the Dull Ember when the player next visits his workshop with the item in their inventory.
The fact that you acquire the Craftsman's Hammer from the chest he is sitting on could mean he is the legendary Blacksmith mentioned in the item's description. Because of this, he could have been locked away in the cell when the Lost Bastille was originally created, as humans feared powerful people.
McDuff may be a prisoner of The Lost Bastille; whether he is an undead inmate, in self-imposed exile or a remnant of the prison staff is unknown, though his situation resembles that of Rickert of Vinheim from Dark Souls.