The Shadow Catcher can be used to “catch” shadows on specified objects.
These specified objects will not be rendered at all.

The “catcher” can be any kind of “StaticMeshActors”.
The chosen material will effect the shadow.

It´s possible to use multiple catcher objects.

Define a Shadow Catcher Object

All objects defined as “Set as shadow catcher object” which are equal to the “Shadow Catcher Objects” list within the Shield Actor, will be used as catcher.

The plane below the mesh object is defined as a shadow catcher object (screenshot in edit mode/not in play)

The shadow will be now added to the render pass

The shadow is also present in the alpha channel