So, here's a thought. Sombra is an Umbra pony that was released from his prison by changing into a regular pony. But in doing so, he lost his memories and changed personality. So what if he wasn't the only one released in this way. Several Umbra could have tried and just gotten lost, it was only coincidence that Sombra ended up where he needed to be. The rest of this faux ponies could have gone on to live regular lives, getting married and having children. Which Stygian could have been one of. So it wasn't so much as he was corrupted but merely used the darkness that was within his bloodline, darkness that used the pain in his heart to try and take control like it did to Sombra. Any thoughts?