Avatar: The Last Airbender - Unaired Pilot

Synopsis
Many elements of the pilot are dissimilar to what eventually developed into the televised series.

(Source: Avatar Wiki)

Background
Background: The unaired pilot episode is a low-budget, pre-production test episode created by Michael Dante DiMartino and Bryan Konietzko with the assistance of Korean animation studio Tin House, to pitch the Avatar: The Last Airbender series to Nickelodeon.

The pilot episode never aired on public television and instead appears as an extra feature on Avatar DVDs with commentary from Mike and Bryan; it is also available for purchase with and without the commentary on iTunes. Many elements of the pilot are dissimilar to what eventually developed into the televised series.

(Source: Avatar Wiki)