Ultra Modular Landscape (UML) is 2 products packed together, available on Fab.com.
1) Next-gen landscape master material using a modular layer system that lets you add or remove layers on the fly with a single click. It has an extensive list of material features implemented in a modular way, with a couple of clicks you can decide if you want a cinematic look with all possible render features or carefully selecting features to achieve good optimization and high performance. The Iceland example scene uses only a landscape material with 5 material layers and no static meshes.
2) Blueprint Prefab System: This allows you to spawn complete mountains, affecting multiple landscape material layers, each using erosion masks. These mountains are integrated into your traditional Unreal landscape system, which means they can be combined and modified in a non-destructive workflow that doesn't consume any extra resources. It supports the Landscape mode's edit layers, you can fine-tune them by sculpting and painting on the layers.