Not sure which quest you are on, but as you progress you will find that you sometimes have to kill four, five or even six enemies before the object you are seeking pops into your inventory. This is especially true in the other worlds (Marleybone leaps to mind). The most I ever had to do was 10 - it was cats in Marleybone, to get an umbrella. Sigh.
it is more random than anything sometimes it takes forever to get it and other times you get it in first fight but what helps if you have afriend that can join you cause youget more monster to join just lake sure to only have the monsters you need join.
On different characters, I've gotten the skull from both Haunted Minions and Rotting Fodders. I've never tried with the skeletons. One piece of advice that I have is that if you are always fighting with someone, try fighting a couple of monsters completely alone. I have two accounts so I am always either with another of my own characters or with a family members' character. Several times when I haven't been able to get a certain quest drop from a monster, I've asked the family member to step aside and I usually get the item on the very next monster I've fought. Could be coincidence, but happens too often to *just* be coincidence IMO.
A tidbit: despite it says any undead, I have only had success of it dropping from a ghoul, it doesn't seem to drop from the rotting fodder, or skeletal warriors (I need the armor pieces at the same time for another guy).
This is especially true in the other worlds (Marleybone leaps to mind). The most I ever had to do was 10 - it was cats in Marleybone, to get an umbrella. Sigh.
i hate that quest. i've been killing cats over and over and i still didnt get the umbrella. and the quest didnt give me a chance to deny it either, so i'm still stuck. i must have killed at least 20-25 cats already, and it still isnt working. lol
Like some one else said, it's more random than anything. I've had times where I've gotten on the first try, and other times I've had to fight ANY monster in the dark cave over and over, again and again.
I'm guessing you are talking about the Runed Skull, not ruined, in which case its the former, than just exclude my comment. Good luck hunting for it.