Sonic the Hedgehog 3 Beta - Ice Cap Zone

The interesting thing here is that Sonic is running down the slopes of Ice Cap Zone, instead of snowboarding. The time counter reads 0:00, which suggests that Sonic's starting position was some way down one of the slopes, instead of at the top where he normally gets on the snowboard. It's also possible that the screenshot is a mock-up, like the famous Sonic 2 concept screenshots.

Sprites are from Sonic 2.