This one might be a bit technical:
You can't have Object Buffers/seperate passes for materials in Cinema 4D, only geometry. As we needed flat textures, we needed to key out some parts of a model to use as an alpha channel. This resulted in brightly colored 3D renders looking more or less like this, which we thought looked quite nice.
I have to admit we cheated a little bit for this version as we put in a few elements that we added in post and were never rendered in 3D ;)
Here is the original spot: TRUMF

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