Try dropping the .mob into the new sequence icon to create a new sequence and see how it looks from there, if it looks fine have a look in the info section of each sequence and see what is different.
Just put a compositing tag on the cloner object….and in the render settings click on Multi-Pass drop-down and select object buffer. Save out your multi-pass render and your regular pass render…when it renders out the scene it will make a special pass for the cloner object that you can then use in your compositing program.
My initial thought would be to import a mesh that represents the mountain and then use a cloner object with a sphere and turn on object mode and select the mountain mesh as the object for the spheres to attach to…then you could use an effector to animate the spheres falling into place.
You need to create 2 identical keyframes at 2 points on the timeline where you want the stop to occur. Then you will need to go into the FCurves and select the 2 keyframes and select Clamp…this should stop the moving about.