The labyrinth sequel was not so much a fake, but rather the construct of 'Chinese Whispers'
An english student at some university had drafted up a basic plot overview (a good few pages worth including some scenes in detail) and cast list, and was required to produce concept artwork for a project. Naturally as soon as this found it's way to the internet it became distorted, misquoted, rehosted, and repeated etc ad infinitum.
Soon enough there was a huge clamour about a Labyrinth sequel, unfortunately all founded on the online equivant of 'hot air'.