I made a couple of GIFs using Trapcode Mir. Just for fun! And to understand how to make them. From a quick search I found that tumblr GIF's have to be less than 1MB and no bigger than 500*500px so that's what I aimed for. I used low framerate (7fps) in AE and 6 seconds for a total of 42 frames. I exported .mov from AE and opened in Photoshop and used Save for Web to make the GIF.
Here is the AEP.