Sonic Advance 2 stage made for MUGEN by Eli King/XCB. It is also very big, as author noted in readme file.
Those who lived in 2000s may recognize this stage as the one featured in Ultimate Flash Sonic, though the stage was likely made a year before UFS became a thing if file dates are any proof of it.
(and yes, if you think only TheIranSonic made this stage (which can no longer be downloaded), Eli King already made one before)

Animated: No
Alternate variations: No
Music: No