Blender Secrets: Inverted Hull Toon Outline (updated)
I decided to update this inverted hull video, since the interface of Blender 2.8 changed and a lot of people asked me where the Backface Culling option went. So here we go.
Create a base color material. Go to Render View and increase the World brightness so you can see what you're doing! Create a second material for the Outline. You can use an Emission shader or Toon shader for the Outline material. In the material settings, turn on "Backface Culling".
Add a Solidify modifier, check "Flip Normals". Set the Material Index Offset to 1 and play with the Thickness to get the Outline. To render turn off Overlays and can go to View and choose "Viewport Render Image".