The name comes from the Chinese term "yao guai" (妖怪), which translates to "monster" or "demon." The name was given to the creature by the descendants of the Chinese that were living in internment camps at the time of the Great War.
The yao guai is a mutated bear of debatable origin species in the Commonwealth. Possibly mutated from the black bears native to the region, these yao guai are generally larger than their unmutated predecessors and are more aggressive.
The physical build of the Commonwealth variant does not seem to drastically deviate from pre-War bears as much as the yao guai in the Capital Wasteland and Zion Canyon. Comparatively, they are overall less dog-like in their posture and movement, sport thicker patches of fur and more body fat. Since their upper body, chest and arms are not as massive, the Commonwealth yao guai have a more traditional bear-like posture and gait.
Although generally found alone, yao guai exhibit a gentle, familial bond toward one another when found together, provided they do not feel threatened by the observer's presence. Yao guai will attack nearly any other creature or person they encounter, including deathclaws.
They seem to appear as often during the daytime as they do during the night. This is a primary difference between the Commonwealth yao guai compared to the Capital Wasteland variants which are more nocturnal in nature.
These creatures also have the ability to cause, unlike their Capital Wasteland counterparts, the staggering effect on every one of their attacks, even if the player character is quick enough to block them. For this reason, melee fighting against yao guai might be difficult, especially with slow weapons such as the super sledge, and if fighting against a group. Attacks must be properly timed, otherwise the player character might get stuck in the stagger effect, giving yao guai enough time to strike once again.
Not as physically imposing as normal yao guai due to minor malformations, past injuries or arrested development. As a result, they are less of a threat compared to other variants. Wherever they are found with another yao guai it is usually one with a similar affliction.
The young yao guai is a variant of the yao guai cut from Nuka-World. Based on the name in the editor (DLC04POISC11_EncYaoGuai), it was planned to appear at the yao guai cave to the northwest of the Nuka-World junkyard. The young yao guai is identical in appearance to a fully grown yao guai.
The typical form of a yao guai, they are stronger than their stunted counterparts and can prove a difficult fight for low level player characters due to their considerable strength and aggressive nature.
A ghoulified version of the yao guai, added to the game with the Far Harbor add-on. Its sensory organs seem to be heavily damaged due to radiation poisoning, age and past injuries, as they have 7 less perception than their non-ghoulified variant.
This variant of yao guai was an addition included in Far Harbor. These yao guai are sickly green in color with hard, bony growths sprouting from their bodies, including near their eyes. Irradiated yao guai are more perceptive than their other yao guai, rendering them a capable enemy.
The rabid yao guai is a yao guai that has been infected with Rabies or a similar illness. In appearance, it has red welts dominating its sides and face, giving it a diseased look. Despite its unhealthy appearance, it can prove to be a deadly adversary in combat.
The deadliest yao guai variant in the Commonwealth, it has a darker coloration compared to typical yao guai. Additionally, it has more pronounced scars on its body. Sporting a large health pool and powerful attacks, it can be an issue for the player character at any level. Those unprepared for such an encounter can meet a swift death in just a few strikes.
Dusky yao guai level with the player character and are therefore immune to the Animal Friend perk.
A yao guai encounter is quite uncommon on normal difficulty. In lower difficulty modes, they are usually found on the western side of the map around Fort Hagen or west of Diamond City. On Survival mode, yao guai can spawn on the outskirts of Concord.