This is a hack for the Sega Saturn port of Sonic 3D Blast which cuts out the main game and allows all seven Special Stages to be played consecutively.
Credit to @bbayles for making the hack:
Twitter / X - https://twitter.com/memory_fallen
Website - https://www.bbayles.com
The original programmer of the Genesis/Mega Drive version is working on an unofficial patch to fix some of the more frustrating elements of the game, add save functionality and much more! Looks pretty epic so far!