This page may contain spoilers for the whole novel.
In some of the translation, the personal pronoun used is "it", but this wiki uses "he".
鬼面 Guǐ Miàn (鬼 guǐ = ghost, 面 miàn= face)
Ghost Face is an immortal entity, a demon. He is the main antagonist of the novel.
During his first appearance, he is not described at all, except that Zhao Yunlan looks back and forth between Ghost Face and Ghost Slayer in confusion, implying that they look very similar. ("Zhao looks at the Ghost Slayer, then back at the person, and he is confused... he has never heard of anyone like that before." - chapter 40)
The only description of Ghost Face, and apparently his only recognizable characteristic, is that he is 'wearing a pale ghost mask.' The mask can change shape, mimicking facial expressions. (chapter 40)
It later turns out he looks exactly like the Ghost Slayer. (reference needed)
He is a demon, but - along with his brother, Ghost King - has a special role among demons. (reference needed)