Yōkai are creatures based on Japanese folklore and mythology. Westerners would consider yōkai to be ghosts, monsters, or at least supernatural beings. They cover a wide variety, with some being mischevious similar to Loki; some being malevolent; and others preferring to be good or at least neutral.
Yōkai can be thought of as a pantheon of beings akin to Lovecraft's Cthulhu mythos, except with the weight of hundreds of years of retelling. The Japanese culture has a different sensitivity to what is creepy or strange. For example, the movies The Grudge and The Ring were both based loosely on Japanese movies that did well. Their horror tends to be more atmospheric than that of the Western countries.
One can find tales of yōkai in many forms, from movies to books to manga to anime. Indeed, many of the American audience members met their first yōkai in an anime. If there is a character that can change shape and tends to be mischevious, it's most likely based on a form of yōkai.
Shapeshifting is one of the most common traits. Some yōkai resemble animals, like a nine-tailed fox, or combine human and animal characteristics.
Many Americans in particular discovered yōkai through the anime series Inuyasha and the movie Sen to Chihiro no Kamikakushi (Spirited Away).
Iron Noder 2017