Neck

The neck is a shapeshifting creature that lives in rivers and lakes. They may take form of any fourlegged creature, although some forms are easier for them than others. They typically choose a human form, or that of a small horse with a long neck. They will, in most stories, atempt to lure people away from home with their song or music. If a person grabs onto the creature or tries to ride it's horse form, they will be bound to it, and the neck, can then proceed to throw itself into the river in order to drown the unfortunate soul. They are however not always malevolent.

Source
While similar creatures have origins predating the neck, the earliest mention of necks, go back to the german epic poem Nibelungenlied.

Media
Necks appear in the following media:

Games

 * Gems of War