As pointed out below, (and sorry for the slow reply), yah, we're clashing each of our IPs together in this game, and instead if basing it on one of them specifically this cyber-world-ish middle ground is where we ended up basing the whole thing, and we can branch out from there.
It's mooostly characters, specially lately, but I do some environment stuff now and then. And yeah, this project is definitely a lot of fun because we get to do both ends of the spectrum, the sci fi and fantasy stuff
Because magic? Also, those talon-like parts close to the middle where his hands are, I bet those still hurt, not to mention cut well enough. Though, I don't see why there isn't any cutting edge right in the middle, since that would allow a very long uninterrupted slash, not to mention it would also look good, and make more sense. Keeping in mind game characters and other designs don't always need to make perfect sense, at least when it comes to something clearly fictional, I guess we can just say "Looks pretty good, but could make more sense while looking better still.", right?
Trying to rationalize something fictional or something that isn't rational to begin with isn't the best way to spend your time.
Illidan had some demon powers even before he consumed the Skull of Gul'dan. Sargeras took his eyes and replaced them with magical ones, as well as marking him with those tattoos. Combined with Illidan's talent for magic, it wasn't hard for him to use demonic magic after that.
He also had the eyes and tattoos at one point before he consumed the skull. Go ahead and take a look at how Demon Hunters looked in Warcraft 3, you'll see he had those. All the skull mainly did was making him bigger, give him hooved feet, wings and horns.