Switching from face to face (or mask to mask).ДЄang and friends are pulled down into a swamp by (an as yet to be properly explained) tornado in 'The Swamp', Aang met Hue. He eventually finds Koh under what looks like a giant dead tree.ДЄ monstrous creature seemingly half giant centipede (a Japanese symbol for evil and the world of the dead) and half schizophrenic Noh performer. A being who would know the mortal forms of Tui and La.

While in the Spirit World, Roku tells him to find a dangerous, ancient spirit named Koh, the Face-Stealer. It's the only time the Spirit World has looked this way. Interesting that, as opposed to his previous trips to the Spirit World (in 'The Spirit World', 'Avatar Roku' and later on in 'Avatar State'), this world looks like a swamp. In 'Siege of the North', Aang travels to the Spirit World, looking for help/guidance from the Spirits in attempt to save the North Pole and stop Zhao's Fire Nation fleet. In response to iyuna_sama's thoughts, I had replied with my own crazy theory (this is my further attempt to convey my thoughts on potential for canon Aang/Toph in a somewhat coherent manner) about Aang's trip to the Spirit World in 'Siege of the North' in comparison to Aang's experiences in 'The Swamp'. Before you proceed any further into this piece of craziness, I'd suggest you go back and check out iyuna_sama's earlier post/theory (and comments, thereof) which discusses a possible connection between Koh, the Avatar's past love and Toph.

Avatar the last airbender spirit world