I'm wondering if this arm is supposed to hint at something, or if it's a brand new concept.
When I first saw it, I thought of Midna for some reason. Though it doesn't look like her.
It seems that Link is somehow controling that turquoise hand. Gamexplain has uploaded an analysis of the trailer where you can clearly see how Link uses some kind of power with his hand that turns it to a very similar colour. What intrigues me is the fact that the "hand" over the dead figure, the one Link is supposedly controlling, has claws in the shadow over the wall. Can this mean that Link will have, or will transform into, some sort of evil "alter-ego"?