(Snip)
My username is like a blind guy. A distinct lack of is.
When I said trailer, I guess I really meant advertisement.
I happened to look up the trailer out of curiosity, skipped to the end, and did see the scene you were talking about.
The nun entering in from the side rather than revealing herself when approached (after the buildup that implied the figure in the robes was the nun) was a definite unexpected thing and not "oh I know what's going to happen next" kind of affair that'd make me sigh loudly. I agree that the scene you dissected was a good jumpscare in the sense that I don't see that as cheap horror.
But that wasn't what I was talking about. Like I said, when I said "trailer" I really meant advertisements. The five-second ones that appear before or during Youtube videos.
I can't link to any of them since they're ads and I can't find any recordings, but I can give a description of the two I've seen so far.
1: A shot of a somewhat dark, but empty hallway. After a few seconds, a Windows Vista loading icon (the one of the circle with the little spark in it swirling around, that replaces your mouse cursor) shows up for a few seconds, before the face of the titular Nun appears. Then the movie reveal (the part where they say the movie's title, show release dates, etc.), and the ad ends.
2: A shot of a black screen with a Volume icon similar to an iPhone's volume icon. The volume lowers a few notches, then increases. Then Nun Jumpscare happens. The movie reveal, and the ad ends.
Your dissection suggests there is was a good deal of planning and forethought into making the end of the trailer's jumpscare scary.
However, I see none of that in the advertisements I saw.
If the forethought present in the trailer jumpscare is present throughout the movie, then the ad jumpscare fails to properly express that.
If the forethought present in the trailer jumpscare is not present throughout the movie, then... Well, the ad jumpscare doesn't really explain a whole lot. Just elicits a reaction more than anything else.