Creating an animated gif using Gimp

Here's a few frames taken from Balls Abound.

I created this with Gimp. 

There are 120 source images taken from a set I made earlier when producing video from the game.  Using "Open as layers" I opened the source images into a Gimp project and now have a set of layers with the ball running from left to right.  I then duplicated the Gimp project, deleted the first and last layer, and reversed the layer order using the layer stack menu.  I then save the duplicate project as an xcf file, and return to the first Gimp project which has the original 120 images in order.  Now using "Open as layers" again I open up the xcf file (with 118 frames in reverse order) and finally I have 238 frames of the ball running left -> right -> left.  Now it's a simple matter of scaling to your desired size, dithering down to indexed color, running the animate for gif optimizer, and save your gif with 16ms between frames (for ~60fps).

One day I will make the effort to brush up on my Gimp scripting (another language I have no capacity to retain once learned) and make this easier on myself.