Sonic X-treme - Wikipedia

Fans Resurrect a Long-Lost Sonic the Hedgehog Game

FNF Vs Sonic.Exe Rerun Executed Prey Fight or Flight X-treme by MattzoDAR on Newgrounds

I found the most well-known Sonic Iceberg underwhelming, so I took my own crack at it. : r/SonicTheHedgehog

Original Never-Before-Seen Screenshots of Cancelled Game 'Sonic X-treme' Unearthed - Games - Sonic Stadium

Sonic Saturn (lost build of cancelled Sega Saturn prototype of platformer; mid-1990s) - The Lost Media Wiki

Sonic X-treme Similar Games - Giant Bomb

Sonic X-treme, Sonic Wiki Zone

Super Sonic (lost build of cancelled Sega CD port of Sega Genesis platformer Sonic the Hedgehog 2; existence unconfirmed; 1992-1993) - The Lost Media Wiki

Sonic Xtreme Prototype - Colaboratory