The Yuyan Archers were a group of elite, extremely proficient Fire Nation archers. By 100 ASC, they were under Colonel Shinu's command, and used to guard the Pohuai Stronghold. The Yuyan Archers were used for very stealthy missions where precision and accuracy were vital for success, and they were one of the Fire Nation's secret weapons.
In the winter of 100 ASC, Commander Zhao approached Colonel Shinu, seeking to use the Yuyan Archers to help him capture the Avatar. After being turned down, a messenger hawk came to Zhao, carrying a letter informing him that the had been promoted, and was now an Admiral. This put him above Shinu, thus allowing him to take control of the archers and employ them in his hunt for Aang. When the archers discovered the Avatar, Aang's extreme agility was matched by their expert aim. Outnumbered and simultaneously trying to collect frozen wood frogs in order to cure Katara and Sokka of fever, Aang could not resist the group and was consequently captured. One archer was later instructed to incapacitate the Blue Spirit.
Their uniforms, especially the short jackets and poofy pants, resemble Zouave uniforms from the American Civil War, which in turn were inspired by 19th century French Zouave uniforms which also were widely imitated by forces of other nations in the 19th century.
The small triangle that is present on Yuyan head bands, and also on Lo and Li's hair bands, is the alchemical symbol for fire.