A Yongma (or mythical beast) is a creature that often acts as a helper and companion for a specific Chachaoong. The power to control a Yongma is an inborn skill which not all Chachaoong possess. Most Yongma introduced thus far seem to have a humanoid form (though some have a beast-like form as well) and none appear to be capable of speech. Some Yongma have personalities and are capable of independent thought and action, while others are little more than tools to be used by their Chachaoong.
And just as it is unheard of for Chachaoong to be twins, it is also unheard of for two Yongma to be the same or have the same abilities.
Yongma's abilities (and personalities) vary as much as those of the Chachaoong. Often, however; their abilities are reflective of their form. Mu-Young's, for example, is a shadow, and often travels with him as such. Yongma are usually at their master's side, but some can freely move about if they wish. For this reason they are sometimes used as scouts or used to relay messages to other people. They are often capable of transformation and interacting with the human world, though to what extent may be limited to their abilities. Almost all have some kind of physical form, though there are exceptions, such as the yongma of Ha Na Rin, which is in spirit form only.
Though some Yongma are capable of communicating with gestures and the like, none have been shown to be able to speak (though Shadow and Shade have been seen growling and making other non-verbal vocalizations.)