Shortly before the end of the Hundred Year War, Piandao provided Sokka, Suki, and Toph with one of these creatures to transport them to Ozai's airship base in order to stop the Fire Lord's airship fleet, affirming that "nothing [ran] faster over land, or [swam] quicker". The eel hound quickly crossed the Earth Kingdom and swam toward the base, allowing its riders to board the departing fleet at the last moment.[1][2]
The eel hound is a large, amphibious lizard that exhibits the ability to swim and run very quickly. It is at least eight feet tall and roughly twenty-five to thirty feet long with dark green scales (except along its ventral side) from its jaw to its tail. The eel hound is green in color with a lighter shade on its underbelly, and a darker shade of green on top of its body.
The eel hound has a very wild nature which can make it challenging to train. For this reason, very few people attempt to do so, and as such, they are not as commonly used as other animals, such as ostrich horses, for steeds.[3]
The eel hound is a tame, calm animal once it is properly trained, and can be used for transportation over large bodies of water or running on land at great speeds; it was credited by Piandao as being the fastest known animal over land and water.[1]
The eel hound is a cross between a greyhound and an eel.[3] With its long, powerful legs, deep chest, flexible spine, and slim build of the greyhound combined with the elongated neck and tail of the eel, it slightly resembles a gigantic greyhound and can run at similar speeds.
The eel hound served as a deus ex machina in the final episodes to facilitate Sokka, Toph, and Suki's rapid movement from Ba Sing Se to the Fire Nation airship base.