This is a progressive quest that gives you acess to other parts of the castle. Yes some of the mobs are hard to find because they are in hidden areas the only way i found them was to do it in order as best I could and if all else fails ask guild lol
He gave me a quest called TRINKETS OF THE DEAD when I hailed him (I was a level 40 Paladin) - perhaps the quest he gives is level/alignment/class etc dependant???? I have since deleted this quest a number of times to see if he gives me a different quest and he doesn't! I have been unable as yet to complete one of the steps of the TRINKETS quest as I cannot find the required mob!