The artist is Ron H. Bruhn, AKA calfCut on deviatART. A big thanks to him for allowing us to use it. I looked around on deviantART for quite some time to find something that looked like it ate flesh and had the right color palette for a black card. Eventually I stumbled on this one
I decided to go with "Wiitigo" rather than "Wendigo" to match Magic's two previous cards that made use of the wintery cannibal demon, Wiitigo and Shape of the Wiitigo. Many monsters from Native-American folklore have a large number of possible pronunciations and variants, so why not match the one that Wizards used?
This was actually a bottom-up card. One piece of design space that is unique to Horde is that the Horde deck has token cards in it. This little guy peeks at the top card and om-nom-noms it if it's a zombie token to regenerate. The double-black mana in the ability cost was chosen so that this ability wouldn't get spammed and used to just do extra damage to the Horde. Hopefully it will fare well in playtesting.