Magister Vlasty:
To find these dark horrors, you should go to the swamp area southwest of the village.
But it may be hard to find a perfect, whole skull. In most cases, when a dark horror dies, the power of the black magic that supports its life is scattered, and the bones are shattered. So, it may be difficult to find a Perfect Skull.
But even broken skulls are helpful to my research, and if you bring me broken skulls along with a Perfect Skull, I will reward you handsomely for your efforts, do not worry. However, I cannot base my studies on Cracked Skulls alone, and so I will not reward you until you bring me a Perfect Skull. If you are ready, you should be on your way now.