One of the best chances to stop Sombra you're going to need uprising not in one city but in all of the city no pony should be afraid of the government it's the government that we should be afraid the pony. You're going to need a massive riot like you want to have the Hunger Games in the first movie

So I take it Flurry Heart was brainwashed into thinking she's Sombra's daughter?

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Ded But that would have been a fun angle.