Artist Aleksi Briclot has illustrated many Magic cards, and they're all great.
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 Aleksi was given for Flameborn Hellion:
Color: Red creature
Location: River of molten metal in Oxidda
Action: A hellion (see reference) has just burst from underneath a river of molten metal, splashing it everywhere as it rises up in search of prey. The hellion has metal-edged scales, jaws, or both.
Mood: fierce and unpredictable
The art description also included references to previous Hellions. So here's what Aleksi was working from:
Armed with that art description, Aleksi submitted a sketch to Magic's creative team. Now here's something interesting: Aleksi works digitally, so the sketch looks like this:
Even though the sketch was done digitally, the piece wasn't finished. Here it is after all the finishing touches!
Here's what it looks like in Scars of Mirrodin packs: