Bloody Mary
Historically a ritual encouraged young women to walk up a flight of stairs backward holding a candle and a hand mirror, in a darkened house. Gazing into the mirror, they were supposed to be able to catch a view of their future husband's face. However there is a chance that they would see a skull (or the face of the Grim Reaper) instead, indicating that they were going to die before they would had the chance to marry. Mary Worth was a girl who saw this and was killed for being a witch. So it is said she’d show in the mirror if anyone attempts this and seeks revenge for her loss of her chance to love. She teaches a lesson of to cherish what you have now and not to take the good in your life for granted.
Wendigo
In Algonquian folklore, the wendigo (/ˈwɛndɪɡoʊ/) or windigo (also wetiko) is a mythical man-eating creature or evil spirit native to the northern forests of the Atlantic Coast and Great Lakes Region of the United States and Canada. The wendigo may appear as a monster with some characteristics of a human or as a spirit who has possessed a human being and made them become monstrous. It is historically associated with murder, insatiable greed, and the cultural taboos against such behaviours. He is a spirit taught to native american children to prevent them from being selfish and crafty. Because people who possess these traits are turned into a wendigo. A being with horrible hunger for people with his hunger being based on his size. But everytime he eats, he gets bigger. Trapped in a forever circle of hunger. It is said he comes for you if you say his name three times aloud. This is a warning to always be kind to people no matter who they are. And to respect rules and your family. There have been real life cases of him in historical records. So it is unknown if he is a myth or not.