So this is pretty much the basic process by which I go about painting these WarCraft cards. I painted this one in February. (Download the image to see it larger)
First, Blizzard emails me a short description of the card along with some reference materials. Using that, I'll submit a traditional pencil sketch for approval (Sometimes I'll send them a grayscale value study. Depends on the deadline). Once I get notes back and hopefully a green-light to go to final art, I'll then create a rough grayscale value study which ultimately sets the stage for the final art; definitely the single most important phase in this process. Once I feel satisfied with the values, I'll start throwing color on top of the grayscale using a lot of masks and color layers. Most materials change value as color is added, so care is needed to confirm the original grayscale study still holds up. I didn't have the background laid in at that point, which isn't the smartest idea, but I wasn't sure how much the winged spell effect was going to suck up the remainder of the card space. Next, In the fourth panel, after some tweaking of the FX to look more like the actual effects in the game (I drew the wings in Illustrator to give it a super-crisp edge), I felt like she overdosed on too much of the glow-y FX stuff; looks kind of cool and powerful, but I just wanted to dial it down a bit. This leads to the fifth and final step where I cooled down some of the warm color, edited/finalized the FX, and decided to paint a background to give it a subtle sense of context and perspective. For late stage adjustments like that, it's always a good idea to save your important masks in the channels window in case you need to go back and quickly add or remove things, even on flattened art. Here, I had separate channel masks of the figure, hammer, cape, wings, foreground, etc... Very convenient for revisions, which are usually inevitable after submitting final art. Fortunately I got this card right the first time, so no revision notes from Blizzard, which is nice.
And that's about it! Hope you enjoy!