Ryu-Guheul is a pale, imposing figure draped in flowing black robes. His skin is a ghostly gray-ish white and his hair short and white. His eyes, like other Yongma, have a pale iris--gray in his case--while the area surrounding the iris is black. He also has black, diamond markings on his face above and below both eyes. He wears long, form-concealing black clothes that have what appear to be black decorative strips of cloth clipped to them, though in actuality, he manipulates these strips of cloths and uses them to fight. The high collar of his robe conceals the lower portion of his face and he's usually depicted as expressionless, rarely seeming to react to things around him.
Taciturn and submissive, he displays less emotion compared to other yongma that have their own conscience. He appears to be conflicted with his master's merciless nature, but does nothing stop him even when he is the one being hurt. In flashbacks, he is shown expressing more emotion openly by having affection towards small and cute things like birds and children. Ryu Guheul has also been shown displaying shock and horror at Bi Gak's actions, such as when he killed Ga Be and Ga Ram.
The only combat ability Ryu-Guheul has demonstrated so far is the ability to manipulate the cloth clipped to his hair and clothing, using them almost like blades. Though they appear flexible like cloth, they are strong enough to impale people as well as block swords. They are also dextrous enough that he was able to wrap them around Ei-Mae's swords and remove them from his body.
Like other Yongma, he appears to heal quickly and easily from injuries that would be fatal to normal people.