This object reference is used to construct the shadow for this object. If this field is blank, no shadow is created for this object. Unless "Check Below Only Once" is enabled, shadows are very expensive in terms of CPU usage, so shadows should be used with care.
Check Below Only Once
If this flag is checked, the z-position of the object is only calculated once-at level construction. The shadow will move in the x and y-axes regardless of whether or not this flag is checked.
If it can be assumed that an object's relation to the ground will never change (i.e., not move), then valuable processing time can be saved by fixing the z-position of its shadow. As a rule, if the object is set to Anchored, and nothing can pass between it and the floor, Check Below Only Once should be enabled.
Scale Based On Height