If there was a way to setup onion skinning ON/OFF button, that would allow us to see previous frame or previous X-Frames (numerous) before or after the current keyframe, even if it was a basic shadow or color. In other animation softwares, I can set onion skinning to any number of frames, especially with vector programs, and this helps so much in determining where to position character poses as per the 12 principles of animation suggestions of inbetween animation.