it's a yellow Belly Ogre viewed from the side...
The Black Goblins, are better organized than their weaker cousin the green goblin that populate Cyrodiil more. As opposed to a green goblin tribe where an archer or a warrior look exactly the same, the Black goglins are organized and their armor will tell you who they are, and also make a real difference in how they are protected. They see their green cousins as low-life and are highly aggressive toward them.
I modified the goblin head following what I always liked of goblins in famous stories, like Legend, LOTR, Labyrinth, an I tried to take that as an inspiration for theses ones. Compared to the vanilla green goblin, the one I made look a lot more evil and mean, something that will add a nice difference between the two species.
Gargamel
And the Smurf Village
