The banshee is a common undead monster in many fantasy role-playing games.
A banshee is the spirit of an evil elven woman. They appear as a floating glowing parody of their former self, (usually appearing ancient and withered, much like the librarian ghost in the movie Ghostbusters). A very rare variant of the banshee will keep all of their former looks, but all of them have a terrible hatred burning in their eyes. The banshee glows brightly at night, but appears semi transparent during the daylight. They are usually clothed in a tattered rag of a dress, that moves as an extension of the banshee's emotions.
The banshee usually lives in abandoned ruins or caves, staying inside during the daytime, while leaving their lair at night to seek out the living. The banshee can sense the presence of living creatures within 5 miles, and she will seek them out and destroy them. The banshee is very methodical about her hunting, over time she will seek out every living creature within her range, killing them one by one (lesser creatures are killed by a mere touch). Intelligent creatures are stalked one by one, and are killed with the banshee's horrific wail. The banshee's wail carries for miles, it can inspire fear even at the outer reaches of its range, but at close range it can drop a person dead in a moment. The banshee's wail is either completely effective instantly, or doesn't work at all on a particular creature. The wail of the banshee also has a long term effect on any plants in the area, killing smaller plants, and causing larger ones to become twisted and diseased. The plant life and general life in the area is usually a tell tail sign that a banshee has a lair in the area.
A banshee can only be killed with an enchanted weapon, holy water, or by magical spells (which they are highly resistant to). A particularly powerful and pious priest can often destroy a banshee with his cross (or other holy symbol). But, any method of killing a banshee requires surviving its powerful death wail (which will slay most lesser men instantly). On a plus side, the lair of a banshee will often be littered with a fortune in gems, jewelry, and magical items taken from it's previous victims (this hoard may have been building up for hundreds of years).