I've been playing with the animation app called Doink
and combining it with green screen FX in iMovie. Below is a short video showing a layered animation over still images.
There are SO many possibilities for this technique.
I created this tutorial showing the iPad steps for making an animation in Doink, the steps I went through to use that animation as a video layer in iMovie over still images and video. See below or at this link
View my other post/tutorial called, The Aliens Have Landed
, about how to make aliens run using Doink.
You can view my students' video all strung together in iMovie at the link above as well.