Sonic Boom (non-existent lost episode of animated TV series; 2014)
Sonic Boom is a CGI-animated TV series based on the Sonic the Hedgehog game franchise, produced by the company Sega of America, Inc. and Technicolor Animation Productions. First premiering in November 2014, it has spanned over 100 episodes in two seasons.
There is, however, rumors of footage from a lost episode of this series.
The person who originally stated this has since deleted his original thread on 4chan, but stated the episode was a pilot shown to Sega of America, Inc., and was scrapped due to it not being "suitable for a first episode". It was never released to the public, but some have theorized that remnants of this lost episode lie in the "Meet Sticks" video.
In this video, there are several storyboard sketches that never saw a release on TV or any other form of Sonic media than this trailer. It is surprising that the sketches have never been released or even been addressed by the artists, yet it remains a mystery.
On August 12th, 2018, executive producer Bill Freiberger was asked about a lost episode of the show. He stated that the storyboards from the "Meet Sticks" video were not from a deleted episode. He also said that the storyboards could theoretically be from a deleted scene of another episode. Still, little information is known about the origin of these storyboards.