Jared really wanted there to be a train, and it did feel right, but in the beginning, I was nervous as to how to execute such an effect or animation. And as you can see in the film, I went with possibly the easiest way of doing it. I constructed the train (remixed from various royalty-free train images) with an angled perspective, key framing it to  move diagonally across the screen. Then, by leaving some time before it enters again,  the audience could imagine it reached a turn off-screen and came back across the screen diagonally. To make it even simpler, snowbanks concealed the need to animate wheels or other moving train mechanisms. 

This download includes the train, background, and snowbank. You can add the Advent Calendar House to complete the setting or create your own scene.