animation - Onion skin wont show unless I draw on the frame, and only shows the lines directly around it from previous frames and won't lower onion skin's opacity - Blender Stack
Add-on: Onion Skin Tools [$] - BlenderNation
Free Onion Skin Addon - BlenderNation
Object Data — Blender Manual
Slash - Add-on for Blender 2.8+ onion skinning animation workflow - Released Scripts and Themes - Blender Artists Community