This is a pretty interesting unofficial conversion of Snow Bros which surfaced in 2012 from a coder called Black Turk.
It’s very rough around the edges, but it isn’t too bad – and looks like a Snow Bros game, though with what seems to be converted graphics and very bad music.
This seems to have been done just out of general interest to see if something could be done on the C64, but there is no intention of finishing the conversion.
Hopefully the coder will shed some light on what made him try to convert this and Sonic to the C64.