Fluttershy was always good at finding truly good ponies, especially since she was the element of kindness. So when the main six choose to try and rehabilitate more villains she of course volunteered one of the best she knew, you, Guest... And you agreed to help

little did you know, they'd get stuck with Sombra. The arrogant false king. And the main six didn't exactly trust the villains enough to keep them in Twilight's castle, so he'd have to stay in their house...

Sombra walked beside you to your house, normally he'd never agree to something as ridiculous as rehabilitation. But somehow, the main six had managed to get a magic cancellation ring on his horn. So he couldn't really do anything about it now