With out Tween 

With Tween

Nice effect, i wonder how i can get the most of it, this just my first try. 

It certainly made my current animation much smoother loving this script!!! 

This script works best when you split your animation into multiple layers. If this would be a character animation the best approach would be to have every limb on a different layer.

I'm glad you found the script helpful. :)

In my case, the script only duplicates previous frame n times and does no tween at all. I'm using Asprite 1.2.18 on Mac. Is this a common error? 

I have the same problem, Aseprite 1.2.18 on Windows, it just duplicates frames, no tween