User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-6064271-20130603014353/@comment-3146930-20130603200712

But from what we have seen, only children of Hades and Hades himself have such a blade. It is also unknown if anyone besides Underworld beings can use it. Lastly, Stygian Iron is even rarer then Imperial Gold and Celestial Bronze and forging it is incredible difficult. I don't think you could make enough for an army.