Kawauso wrote: He was a mere shadow for most of the episode
This is the reason why people don't like him, not because he wasn't powerful.
Kawauso wrote: There is also something I was wondering about the dark magic. Could it be that the dark magic corrupted Luna into NMM or maybe Sombra was the one who corrupted her. It just seems to me that this won't be the last we see of Sombra or at least hear about him. I'm more curious on what Luna's whole deal was during the episodes anyways. She seemed sorta on edge.
I can see this happening. He was already sealed away when she became NMM, but it could be a spell that was put on her before that.
I also saw this rather interesting theory:
Anyone else getting the idea that Sombra might have been Celestia’s former pupil? I mean, he’s kind of like Twilight in how he’s a powerful Unicorn seemingly capable of a wide variety of magic. And Celestia’s test was to ensure that Twilight wouldn’t sacrifice the well-being of others for her own selfish interests. What if some other pony failed in such a regard? And what if that pony was Sombra?
These episodes actually worked really well opening up potential plots.