Re: How to create this pixelation look

I think you're on the right track and I believe the transitions may just be a modified animation preset. Go to Animation>Browse Presets and when Bridge opens go to "Transistions - Dissolves and look at the "Block Dissolve - Random" preset. Double-click it to add it to the selected layer in AE. It has some options for block size and you can adjust the keyframes to get the speed you want.