I understood the issue, but I'm stuck at making it work right.
Here is a capx with the exact same logic as my game: dl.dropbox.com/u/1606950/helpme.capx .
What I need is to check if the cloud is colliding with the blue bar and destroy ONLY the one which is colliding, not all of them like now. The problem is that I don't know how to pick that correct instance.
If there is another solution it's more than welcome, I need the scrolly because it increases performance tenfold on mobile.
Thanks to everybody that could help me.