There are a couple of ways to do this.
The first would be to manipulate the sprite size as it travels along the path. Make it bigger then smaller.
Second, you will need a second sprite to act as the shadow.
First get the ball moving properly.
Then animate the ball growing then shrinking.
Then add the shadow sprite and it's movement.
The other way, would be to make the shadow and ball movement as frames in the animation of the ball.