File:London2012 Shadow.png - Sonic Retro

Sonic Party Video Games

Sonic Team - Sega Retro

Sonic, Fiction Database Wiki

Mario & Sonic at the London 2012 Olympic Games - Sonic Spin-offs - Sonic Stadium

Sonic the Hedgehog (I-Mode, J2ME) - The Cutting Room Floor

File:London2012 Vector.png - Sonic Retro

Mario & Sonic at the London 2012 Olympic Games (Nintendo 3DS) - Super Mario Wiki, the Mario encyclopedia

Artwork of Shadow the Hedgehog, Sonic Art Assets DVD Wiki

Sonic - Super Mario Wiki, the Mario encyclopedia

Sonic the Werehog, Sonic Wiki Zone

File:Shadowth vector.png - Sonic Retro

Sega Retro:Anniversaries/November - Sega Retro

File:London2012 Sonic.png - Sonic Retro

Sega Retro:Anniversaries/May - Sega Retro

Due to the lack of a proper timeline in the Sonic Encyclo-Speed-ia, I decided to make my own. Second image contains my notes, reasonings, and conjectures. : r/SonicTheHedgehog