Kyatric can you help with that?
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Well, after many searches and many attempts, i've figured out how to do. Actually it's very simple.
With your "to scroll" background (in this case a starfield) taller than your static background, you just set Layout properties> Unbounded Scrolling>yes
And now, the reverse sentence should work.
System on every tick: System set scroll Y to scrolly - 8 (or any speed variable) *dt
**I didn't implemented the loop yet, but should be not too difficult.
Thanks for the attention!