tracing in illustrator

First of all I drew my characters as shown in previous posts, I then opened them in illustrator and traced around them, each feature including background colour, and outline, having it's own individual layer.

I did this with every one of my drawings, and was able to tweak them a little without redrawing them all, to add movement, then exported as a .png file, with a transparent background. However I didn't cotton on to how to do that until I reached this part of the animation, so the zoom-ins at the beginning didnt have this. I was going to go back and change it, but I didnt think it needed a background as it's just introducing the characters, and the background is to help show movement in my animation. 

background:

but to make it more in the background, I gave it a 50% opacity.