Crossover with Supreme Commander

There are many legends in Equestria. Those of Nightmare Moon and her terror upon the land, Sombra's enslavement of the frozen north, Starswirl's many feats of magic. Now, many of the old legends are either forgotten or believed to be stories for foals. But there are a few that are true. One of those is that of the Triumvirate, a group of three-obviously-mercenaries that wielded weapons not seen before, and capable of commanding armies with ease Through time, the whereabouts of two have faded, their fates unknown to all but the few who were there to last see them, including the last of the three. Now, one thousand years after the Triumvirate was no more, a shadow looms over Equestria, one which not even the Elements can combat, and only legends of old have a chance of defeating.