Sonic Jr. (lost build of unreleased Sega Pico game; existence unconfirmed; 1994)
After the release of Ecco Jr. for the Pico and Genesis, SEGA announced other games based on younger versions of its characters. Amongst those announced was Sonic Jr.
The game was announced at the same time as the release of Ecco Jr., and this one would have likely been similar in concept. However, no more "Jr." games were ever released after Ecco Jr.. Whether the eponymous Sonic Jr. was a new character (possibly Sonic's child) or simply a younger version of Sonic and what Sonic Jr.'s gameplay would have consisted of is unknown. In fact, it's unknown if any development for the game was done.
It could be possible that it was quietly cancelled when Ecco Jr. ended up not being a big seller for Sega, or was a simple publicity stunt, or even a hoax. The game still remains a mystery amongst Sega fans, and whether or not it'll ever surface is a mystery.
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- Sonic Retro page on Sonic Jr. Retrieved 11 Apr '15