Challenge: with this topic it would be neat to extend the play for the "sledders"
avoid flapping birds or snowmen etc.
1 thing that I learned with this exercise is that if you adjust friction on both your invisible terrain pieces and your sprite you can get a great sliding surface.
adding controls in a game on screen to adjust the physics in game play will be fun and that can be accomplished by creating slider for the physics properties.
Also used web fonts in this one too.