Before Luna became Nightmare Moon, there was Discord, and before there was Discord there was Sombra, the tyrant King of the North. He was the only foe who was vanquished without the Elements, but by the Two Sisters with divine magic all their own. They lost a city; it was taken by the mad king's magic.

After years among the three pony tribes, the Two Sisters fight their first great foe all by themselves: King Sombra, the tyrant King of the Crystal Empire. Nothing goes as planned, everything, and everypony are not as they seem.

The price for this oversight is the future.

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