Playing Fog on the Barrow Downs. The "main staging" area has a trap. A player defeats their private staging area with 1 enemy in their staging area and we now have to combine staging areas. Does the trap attach to the enemy? The trap says, "next enemy that enters the staging area" -- so is that enemy entering the staging area, or is combining different?

Should be the same. At least I´ve not encountered anything suggesting those concept shouldn´t be interchangeable in this way.

Sounds good. To me it seems he's already a part of the staging area -- it's just getting bigger. But I like your ruling better.

Think there may be a difference as to whether the trap or the enemy is being added to the staging area. In your example where the trap is in the main staging area, it is the enemy who enters it and thus get the trap attached. Had it however been the enemy who was in the main staging area and the trap that was being added, I would rather think the trap behaves as if it had just been played from your hand.