1. Art Description
The art description establishes the parameters of the artist's task. It provides details of what the card will do, what its flavor role is, and what the mood of the illustration should be. Here were the instructions given to Nottsuo for the project:
"This artifact creature has four legs and four arms, and its head has a face on each side. The creature can split into two creatures when attacking, each with two arms and legs."
Inspired by Legends' Stangg, the flavor behind Gemini Engine's Twin-token mechanic is that the Engine can break into two pieces equally capable of combat. There's a lot of room for experimentation here for Nottsuo, an artist new to Magic (who also illustrated Darksteel Brute and Wirefly Hive in the Darksteel set).
Here's Nottsuo's initial sketch.
Gemini Engine sketch by Nottsuo
Note how the Engine actually has two separate heads here. The art team wanted more indication that the Engine could split apart right down the middle, with one head that could split into two halves. Also the reddish tint of its metal skin needed to turn into a more silvery-metallic color, since the card has no affiliation to the Magic color red.
3. Final Art
Here's the final art as submitted by Nottsuo, taking into account the art team's desires.
Gemini Engine final art by Nottsuo
Finally, here is the card as you can see it in booster packs.