Step 1: Create the body
Overinflated it so it was big enough that my son could fit inside.
Then we paper mached the whole thing with 3-4 layers. I found it was easier to just rub the paste all over then stick large sheets of newspaper on top the rub more paste on that.
We had it sitting on a bucket that served as the opening in the bottom.
Once it was completely dry just deflate and remove the yoga ball.