Bungie likes hiding things in plain sight. They've never explained this postcard image, which is very very odd. For one, it's the only time we've seen mixed enemy factions in any asset given to us by Bungie. For another, they do not have weapons. More obviously, they are glowing inwardly with an otherworldly glow, and that smoke surrounding them? Seems clear that something is controlling them like puppets. A fifth race, more sinister than the others, that doesn't have a physical form but instead controls others to accomplish its worldly biddings, would be a very interesting addition to Destiny.