The shadows from persona 4. I'm calling it right here, right now. Every hero has a shadow that is their opposite but still tied to them somehow and is evil, and Stigma is just the shadow of Overlord man or whoever is on the space station, and the secret 4th act twist is that he was a villain all along, and stigma really was the opposite of him and was trying to work for world peace. Either that or they are shadows created by Stigma, to be the perfect nemesis of every hero, and eventually kill them.