Okay then, what am I missing?
It must to be made entirely in Wings3D (but, you can use any image software to create the textures); Check.
You can use old works or make completely new ones. Avoid to create many variations of the same work; Check.
Submissions must to include a screenshot of your work in Flat shader mode and the splash screen image with size of 620x348 (16:9 aspect ratio; The image can be a screenshot of the Geometry window, but respecting that dimensions); I don't know what "flat shader mode" is, I don't play with the internal view settings much. Image size is check.
The rendered image must not to include any Wings3D's logo and it must be in PNG format; Check.
No post production allowed; The only "post-processing" is putting the two images side by side. Perhaps this is what you don't like?
It must to be made entirely in Wings3D (but, you can use any image software to create the textures); Check.
You can use old works or make completely new ones. Avoid to create many variations of the same work; Check.
Submissions must to include a screenshot of your work in Flat shader mode and the splash screen image with size of 620x348 (16:9 aspect ratio; The image can be a screenshot of the Geometry window, but respecting that dimensions); I don't know what "flat shader mode" is, I don't play with the internal view settings much. Image size is check.
The rendered image must not to include any Wings3D's logo and it must be in PNG format; Check.
No post production allowed; The only "post-processing" is putting the two images side by side. Perhaps this is what you don't like?