NOTE: Artworks shown below are not known to have a direct relation to particular game installments of the Mario series. Some were featured at specific events that Nintendo was involved with, while others have been used for various purposes by Nintendo.
Mario Portal
Shaded artwork
Artwork from Christmas-themed pop up card printable from Nintendo in Japan's topic
Artwork from "DIY Paper Craft Holiday Tree Ornament" printable from Play Nintendo
Artwork from "DIY Paper Craft Holiday Tree Ornament" printable from Play Nintendo