How do I create a stationary walk with moving cropped terrain like in the GIF? I can create the walk, but the cropped environment, I can not figure it out.
You can use a boolean modifier on the environment (terrain and assets). If the boolean object (a cylinder) is stationary, and the environment moves, you can achieve this effect. You can even assign a separate material (for the sub-terrain layers) to the boolean object and transfer it to the resulting terrain geometry through the boolean modifier.