The video below shows a way I came up with to onion skin individual elements by using layers, in Krita. It also shows how to use layers to draw motion paths, and block timing. Result
Krita: Onion Skinning Elements
Tag: 2D Paint
Krita: 2D Painting & Animation
Krita is a professional free and open source painting program. It is an excellent tool for concept art texture and matte painters illustrations and comics In addition, is supports 2D animation Get Krita The software can be downloaded from Krita.org