Curse of Strahd
Sometimes the dark forces of Ravenloft are drawn to an area of great suffering. Some swamps, rivers, lakes, or patches of ocean can become such areas when they are used as a site of murder, sacrifice to some dark god or demon, or even if they unintentionally become the place of a horrible tragedy. At those times the powers of Ravenloft can feed and nurture the evil created by the suffering a creature endures when life is choked out of them by the waters of these locales. When this happens the victims of such suffering can rise as a form of undead that remembers just enough of it’s life, and death, that it is driven to seek out elements from those times trying to end the ceaseless agony it endures. These are forlorn creatures, but pitiless in their quest to make others share their pain and perhaps end their own.