I would be Erebos, the personification of primordial darkness. The mask would be similar to this one:

but in shades of dark grey and black. My own powers naturally hide my eyes to where looking into the eyeholes simply shows a deep shadow, as if nothing is there.
My powers would be shadow walk and darkness/shadow manipulation. I would be able to step into a shadow and emerge from another. When looking at me, an observer's eyes tend to just slide off, making me operationally invisible (all they really see is a dark shape and can't make out any real features or dimensions. Walking into a room would cause a noticeable drop in light levels just from my presence, and I can generate darkness so complete that a floodlight can barely be seen from ten feet away. My control over darkness is so complete that I can generate solid objects out of it should I desire, including weapons and shields on par with advanced body armor (think Green Lantern, but with shadows instead of green light).
Despite the shadowy mystique of my powers and abilities, I lean toward the light side, and do not take contracts to do evil. I will take them for justice, but not evil.
EDIT: Nevermind. Apparently someone else had pretty much the exact same idea.