Walking along a plane

Hey guys,

Ok, this is more of a theory question. I am trying to create a 2D environment where the user moves a character across a platform. I am wondering what is the most efficient way of coding this platform, is it best to create an invisible movie clip and create some clipping code between the player and the MC or is there a much smarter way of doing it? Here is a rough diagram to show what I am trying to create, where that blob is the player.