Looks pretty cool, wish you did something different with his stomach though, the guts hanging out don't really fit anything living. The weapons could probably stand to look a little different as well, right now they still resemble giant meat cleavers rather than a troll/orc weapon of some sort, like brutal axes.
Btw, you can force most skins alpha channels to work by using the trigger "Animation-->Change unit vertex coloring" and then setting the value listed as "transparency" to 1%. You might want to try it out with the extra arm and see what happens, I'd recommend using a periodic trigger just in case something sets it off when your testing it. That way, people could have the option of getting a troll with two arms
(unfortunatly this also means all screenshots must be taken in-game :O )