The Gjenganger
The gjenganger is a ghost who has returned from the dead with violent intent. It preys on the sleeping, when it can, spreading disease and death. Unlike many ghosts, it can, and must, be defeated. It cannot be satisfied or reasoned with.
Sometimes, it will prey on a single being for many nights in a row, causing the creature so afflicted to gain exhaustion levels each night as well, if not stopped. As long as no one wakes to fight it, it may be satisfied with a single bite each night.
Like many other undead, its preferred prey are its own friends, family, and neighbors, but it will gladly terrorize and kill anyone who is foolish enough to come near its haunting site, which is often, but not always, its barrow grave. Those unwise enough to sleep within a mile of that place are in for a rough night.