Entry 1: The most ancient spirit in the Universe, Koh is from the dawn of Time and thus quite wise. He appears as a giant, though disproportionately short, centipede. Instead of a head, Koh has a large armored eyelid surrounded by eight jointed legs. Koh is known by other spirits as the Face-stealer, as he takes for himself any face (spirit or living) he sees that shows an emotion. He shows the faces at random inside his armored eyelid; every time he blinks the face changes. Those whose faces were stolen literally lose them, and have no facial features thereafter. Aang meets him in the Spirit World in Episode 20 to ask where the Moon and Ocean Spirits were. Here, Koh informs Aang that it had been a long time since he took a child's face. He also informs Aang that a past Avatar about 800 years ago tried to kill him, after he took the face of the Avatar's love. During this time, Koh showed the face of a beautiful woman. Aang finally got the information he sought and as he left, the face Koh was showing was very similar to that of Iroh's lost son. He also murmured a promise to Aang that they would meet again.

Psychedex Entry 1 written by -Ngo-rongo-ro

Entry 2: Koh the Face Stealer lives in a dark and muggy swamp in the Spirit World underneath a giant tree. He is a centipede-like creature at least 6 ft. high and 30 feet long. His legs are roach-like and a giant eye-shaped head with spider-legs that assumedly takes place as eyelashes. His face, well, duh, it consists of faces that he has ‘stolen’ in which he has the ability to do. A face of a creature, human or animal, is placed in the center of the eye-shaped head just like the pupil is placed in the center of an eye. A face is changed everytime it ‘blinks’ its ‘eye.’

Koh is a very heartless, yet, knowledgeable creature. He is also very old. Obviously, he is the only creature in the Spirit World that has lived the longest to remember about how the Moon and Ocean Spirits moral forms work.

The descriptions of the faces are listed below:

Face #1: A White Mask - similar to the masks of the Japanese Noh.
Face #2: An Angry Man - the face that was shown while showing his anger to Aang.
Face: #3: A Calming Lady - a face of an avatar from the past that tried to kill him.
Face #4: A Monkey - a same face of a monkey that was sitting near Koh’s lair, possibly not the same one. Koh showed this face to laugh. I’m unsure why? Probably to express emotions.
Face #5: An Owl - owls usually don’t show any emotions, so I’m not sure why Koh stole this face.
Face #6: An Old Man - this face was shown when Koh was talking about the Moon and Ocean spirits.
Face #7: Blue Ogres - another angry expression to Aang to show an emotion from him (but it doesn’t work).
Face #8: A Sad Man - the last face shown. Many fans believe that this description of this man’s face may be Iroh’s son who got killed some years ago.

As mentioned earlier, I believe that the faces show emotions towards the rendezvous of whoever is talking to him. Which Aang tries not to react to any emotions or else, face-off.

Koh is only seen on episode 20 “The Siege of the North Part 2.”

Psychedex Entry 2 written by sluggmunki_tx

Other Spirits: