Unaired pilot

The Avatar Series Pilot was a pre-production pilot animation used by the creators to show their idea for what Avatar was going to be to Nickelodeon. Some aspects of it (i.e. the serpent) found their way into real Avatar episodes.

Plot
The Pilot opens with an intro similar to the one in later episodes, explaining the circumstances of the plot. The Show then moves into the story.

Aang, Sokka and Kya, who would later be renamed Katara, are running from Prince Zuko and his ship. While they are escaping, Zuko's Ship is attacked by an enormous Sea Serpant.