Creative Tank

Open TimeLine click the first frame on the onion skinning and Make a shape whatever you like. We're going to change this shape to another.

On onion skinning, choose another frame (ex. frame No.40), Right-click on the onion skinning to open the menu, select "Convert to ignore Key frames" or Press F7 to make a blank key frames.

Create a different shape with first one and This will be the target shape.

On onion skinning, select any frame between 2 key frames. Right-click to open the menu, select” Create shape tween".

If the onion skinning become a green background and with a solid line arrow on it, that implies the shape tween has been made successfully.

Now drag the cursor on onion skinning, you can see the deformation process. This is a screen-shot of the frame twenty.