Prefabs

A prefab is a type of game object that behaves similarly to auto-refresh groups, the difference being that you can't uncheck the "auto refresh" setting. They are primarily used by designers to create game objects with consistent behavior across all levels.

For example, in Metro Exodus all switches, doors, and a lot of other usable objects are prefabs.

We have a lot of prefabs and groups in the game and we use a proxy to destroy the part of a level that the player has cleared and cannot reach again.

Prefabs and groups cannot be attached to other objects but objects inside prefabs and groups can be attached to other objects.

In the Objects List window, select all objects inside a prefab, just like you would, if selecting objects inside a group.

Highlight your proxy → RMB Click → Highlighted → Attach selected to proxy.