Ecco The Dolphin Wiki

The alpha version as it appeared in an Ebay video.

Sentinels of the Universe was to be the sequel to Ecco the Dolphin: Defender of the Future. It was in development for the Sega Dreamcast but was cancelled in the early 2000s when Sega discontinued the console and largely ended first party support. The project was cancelled instead of shifting development to PS2, Gamecube, or Xbox. Other than the mysterious title, not much is known about the game other than what was seen in an Ebay video supposedly showing the game running on a Dreamcast development kit.

In June 2016, a prototype build of the game, dated February 19, 2001, was dumped onto the internet, along with a self-boot, allowing it to be played on emulators or burned onto a CD for Dreamcast consoles. The build features no music or sound effects, and features six incomplete but playable levels. The assets and engine from the Ecco The Dolphin: Defender of the Future are reused, along with many unfinished new assets. No information is available as to the game's intended plot.