Here is a simple example of making pseudo-3D (isometric, perspective) endlessly scrolling background.
Preparing the correct image is the most important part. Don't use "Perspective" tool in software like Gimp or Photoshop, as it distorts the image vertically. Ideally, each cell should be the same height.
Place two instances of the sprite on the layout and enlarge the bottom instance. Both images should connect seamlessly.
The rest is done in the events, see the attached capx file.