Mare (folklore)
A mare (Old English: mære; Danish, Norwegian: mare; Swedish: mara; Polish: mara, zmora; among many others) is a malicious entity in Germanic and Slavic folklore that sits, walks, or "rides" on people's chests while they sleep, bringing on nightmares. When placed on the victim's chest, it is said to have a suffocating effect, and can lead to cold sweats or sleep paralysis. It is often a female being with magical abilities for haunting its victim, including the ability to shapeshift.