Artist Daren Bader is a Magic illustration veteran, having illustrated over 140 cards since Tempest. You can see his work on such cards as Sarcomancy, Oath of Druids, Zephid, Crater Hellion, Sliptide Serpent, Mystic Snake, Verdeloth the Ancient, Deep Analysis, Jareth, Leonine Titan, Silent Specter, Eon Hub, Enduring Ideal, Nezumi Shortfang, Condemn, Woebringer Demon, Akroma, Angel of Fury, and Oros, the Avenger, among many more.
The first step of the creation of a card's art is its art description. The art description tells the artist what the card will do, what its flavor is, and what the mood of the illustration should be. Here were the instructions given to Daren for Riddle of Lightning, called "Future Shock" during development:
Color: Red spell
Location: "mountain" top
Action: We see the hands of a red shaman holding his staff high. The metal top of the staff has magically opened down the center, revealing pages, as if it were an opened book. A bolt of lightning surges from the open spread and hurtles toward the viewer. Focus: the *lightning* spell
Mood: A magical allegory of the power of knowledge to inflict injury on my enemies!
Notes: Daren, find an angle and sell it :) have fun!
The next step is for the artist to submit sketches of his or her vision of the art description.
Here's Daren's initial sketch submitted for Riddle of Lightning:
Riddle of Lightning sketch by Daren Bader
The creative team was happy with the basic composition, but had nitpicks about some of the details. The pages coming from the shaman's staff needed to be a less literal "book," and more of a metaphorical set of scrolls (representing the mage's library). Also, since this is set in post-apocalyptic Dominaria, the shaman needed the traditional red-aligned mage look, gas mask and all. Here's the next sketch:
Nailed it. All that was left was for Daren to send in the final color of the piece.
The final art really sells the concept. Here we can see the runes from the shaman's scroll-staff firing right out with the lightning. When you cast Riddle of Lightning, you are literally blasting an electric bolt right from the power of your library!
Here's the card in its finished state, as you'll see in booster packs of Future Sight. Get ready to hurl your magical repertoire directly at your enemies (with a little help from Daren Bader)!