Yaoguai (妖怪 pinyin yāoguài), yaogui (妖鬼 yāoguǐ, lit. "strange ghost"), yaomo (妖魔 yāomó, lit. "strange devil") or yaojing (妖精 yāojīng, lit. "sprite" or "seductive"), is a Chinese term that generally means "demon". The term is usually used in Chinese mythology and folklore.
Yaoguai are mostly malevolent animal spirits or fallen celestial beings that have acquired magical powers through the practice of Taoism. The evil ones are usually referred to as guài (literally, "freak") or mó (literally, "demon") in Chinese. Their greatest goal is achieving immortality and thus deification.
In Journey to the West, the demons seek this mostly by the abduction and consumption of a holy man (in this case, Xuanzang).
Not all yaojing are actually demons; some others are of quite unusual origins. In the case of Baigujing, she was a skeleton that became such a demon. Many yaojing are fox spirits, or according to the Journey to the West, pets of the deities. There are also yaoguai kings (mówáng) that command a number of lesser demon minions.
In Chinese folklore, the Chinese hell (Diyu) is a place that is populated by various demonic spawns. Most of these demons are influenced by the Indian rakshasa or yaksha and therefore bear some similarity with the Japanese oni.
In Japanese, yaoguai are known as yōkai (actually, the term is a loanword from Chinese; the native Japanese equivalent, sometimes written with the same kanji, is mononoke).
Famous Yaoguai in Chinese mythology:
Baigujing - literally, " skeleton spirit"
Niumowang - literally, "bull demon king"
Pipa Jing and Jiutou Zhiji Jing - in Fengshen Yanyi
Note: Sun Wukong uses this term often to insult his (demonic) adversaries.
The 2008 video game Fallout 3 features mutated bears identified as Yao Guai. These creatures roam the game's setting, a post-nuclear Washington, D.C. and surrounding areas of Maryland and Virginia. They attack both the player and various non-player characters. One of the in-game radio stations broadcasts an occasional public service announcement, reminding listeners "don't feed the Yao Guai". These creatures are also featured in later entries of the Fallout series. The Yao Guai in the Fallout lore were named by descendents of Chinese internment camp prisoners. These creatures appear in the Fallout New Vegas DLC Honest Hearts and in Fallout 4, too.
The Taiwanese black metal band Chthonic has a drummer who wears a metal mask of a black demon mouth.
Once Upon a Time featured a creature called a Yaoguai in the second season episode "The Outsider". Here, it was depicted as a large lion-like creature with a mane of fire. Maleficent transformed Prince Phillip into a Yaoguai until it was undone by Belle.
The Yaoguai's Yaomo alias was used in AdventureQuest Worlds during its 2014 Akiba's New Year celebration on Yokai Island. It is depicted as a horned half-demon half-horse creature (with the build being similar to a centaur) with additional eyes on its chest and parts of the horse body. It was responsible for corrupting Akiba's Jingshen Forest causing the Qilin Senlin-Ma (who was the guardian of the Jingshen Forest) to enlist the player for help. The players were able to defeat the Yaomo.
An episode of the television series Sleepy Hollow features the Yaoguai as a demon who is attracted to aggression and gunpowder.
