For the toon style all the backgrounds are pretty much left stock as they came. For the characters I change all the skin. I start with a preset from the Poser content runtime under "materials/Poser (version) Content/Cartoon/toon/GF-Skin1" and I darken out the diffuse color node. here is a pic

For the clothing i do the same with a preset from the same library and adjust the color if it is plain. If it is a pattern or texture I just add an edge blend to the node. here is a pic:

I delete all the lights and use add one ibl light and that helps flatten the look. if there is a shadow i create that by adding one more light a spotlight and position it above the character to get a shadow. I then turn the preview shadow size to max (4096) It does not affect the flatness just gives shadow. I usually render with preview render. My normal settings are to untick remove backfiring polys and set preview resolution to 2048 (sometimes 4096 but it usually does not make a difference).

Not in this intro but in some scenes the background did not render correctly in which case I render in Firefly with auto setting set to final and no other changes.

note: (sometimes the edge blend on a characters clothes will not show up in a firefly render but only in a preview render. I was told It is because some clothes Items are made flat with no depth. I just then render the character in preview with the background off and composite over the firefly rendered background. Aside from that my characters look exactly the same rendered in preview or firefly but preview render is faster)

One last comment I think the look is really sold because I use toon style hair. I have never been able to get strand hair to look good in a cartoon setting. Also I mostly use anime style eyes and faces on the characters. The four main characters used here are Near Me, Hiro 3, Star!, and Maybe (by Akatora)