Mara (Nightmare)

Mara/Mare/Mora is a spirit that sits or walks on the chests of sleeping men, giving them nightmares. Often depicted as a feminine figure, Mara has several different backstories explaining their reason for bringing nightmares. They're sleep paralysis demons that can potentially kill their victims. They're spirits of evil, revenge, and malicious intent. They're capable of shapeshifting, even turning into beautiful women to torture men with desire before killing them. A bad omen to dream of horses.