Called before the duplicator copies the entity.

If you are looking for a way to make the duplicator spawn another entity when duplicated. (For example, you duplicate a prop_physics, but you want the duplicator to spawn prop_physics_my), you should add prop_physics.ClassOverride = "prop_physics_my". The duplication table should be also stored on that prop_physics, not on prop_physics_my.

See also ENTITY:PostEntityCopy.