Transparent surfaces look incorrect

Set Ambient Shade to 0 for the environment fog light.

Jagged surface edges in environment fog

Do one of the following:

• Turn on Shading Samples Override for the environment fog shape. Increase Shading Samples and Max Shading Samples (to the lowest value that produces acceptable results).
• Increase Edge Anti-aliasing in Render Settings window (to the lowest setting that produces acceptable results).

Outlines around 2D motion blurred surfaces

Do one of the following:

• Remove any transparent objects, fog, and, or glow, and set the background color to black. Render the scene, then composite the elements you removed with the rendered image using compositing software.
• In the Render Settings window, set Smooth Value to 0 and turn on Color.

Grainy or flickering environment fog

Do one of the following:

• Turn on Shading Samples Override for the environment fog shape, and increase Shading Samples and Max Shading Samples (to the lowest value that produces acceptable results).
• Turn on Volume Samples Override for the environment fog shape, and increase Volume Samples (to the lowest value that produces acceptable results).

Break Connection on Environment Fog does not delete fog

If you have turned on Environment Fog in the Render Settings window, and try to turn it off later using right-mouse button Break Connection, the fog remains.

Do one of the following:

Find the Environment Fog material in Hypershade and delete it.