Nyla

Bato of the Water Tribe
Nyla's first appearance was in Bato of the Water Tribe. Zuko hired June to track down the Avatar using Nyla. Nyla is a Shirshu that can find anything with smell. When Zuko found and fought Aang, Nyla fought Appa and wounded Appa with it's tongue. Katara defeated Nyla eventually by confusing her with perfume which she bended out of pots.

The Old Masters
When Aang disappears Zuko takes Team Avatar to see someone who can find Aang. They find June and Nyla at a bar in the Earth Kingdom. Katara hands June a sample of Aang's smell. Nyla turns in circles then covers her mouth meaning Aang does not exist. Instead Zuko has another idea and hands June his uncle's smelly shoes. Nyla sniffs it then takes off to Ba Sing Se where they leave them to find uncle.