I found 2 interesting things regarding background scrolling while I was messing with the values :
(Note 1 : for all intents and purposes, the bytes are numbered considering the first byte as byte 1 and values are in hex)
(Note 2 : the modifications should be applied to blocks 3 and 5 for bottom and top backgrounds respectively)

Disabling vertical scrolling

Works for both top and bottom background

This is achieved by putting a value of 40 for byte 13 and by putting a value of 10 for byte 16.
By doing that the background will stay vertically static to the camera.
Sadly I have yet to find a method to block horizontal scrolling (or at least one who doesn't involve disabling the HDMA).



Automatic horizontal scrolling

Works for both top and bottom background

It only works for backgrounds who already have a horizontal animation, you can achieve this by putting a value of 10 for byte 16 and it will animate the whole background instead of partially animating it.
(Note : if byte 13 value is somewhere between 40 and 4F, this effect will be overridden and instead the vertical scrolling will be disabled)

Nice find!

I remember seeing some similar stuff when messing with blocks 3, 4, 5. Block 4 seems to have the same format as blocks 3 and 5, but affects the level layer itself (I think the scroll options are a bit different or don't work though).

These are the only blocks that still have unknown values that the editor can't edit, after this many years.

Lol.

I wonder, any exact example of a background that has already horizontally scrolling?
That sounds pretty neat. You can achieve some effects like in a level in SMW forest of illusion, in which the background is moving to the left, and you are in some platforms, looking that you are going really fast.
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You nailed it, not just the Cloud BG but really any background that have moving clouds is eligible for the trick.

Well, the moving clouds in BGs are done with parallax scrolling, which scrolls horizontal slices of the BGs using HDMA. I think no original levels use this byte to enable autoscroll on the whole BG.

Maybe during development they implemented this to do the moving clouds, and then they changed it to HDMA?