So I don't have the time to make this story so you can take it.

In the past King Sombra finds the EQG mirror and kidnapped a human child boy or girl to be his heir.
He teach the child in the dark arts and war fare but the child isn't as evil as his "father". At the attack from the alicorn sisters the child vanished with the Empire. As "It has returned" so did the child he was inprisoned by Shining Armor and Cadence because the child is the evil heir of sombra.
You can also post ideas you can't write down and I hope this story finds a good home.

Edit:The child is still in human form and it would be a bit more interesting if the child was female.

3294766 I think your idea is great. I love it when a hero gets treated like an antagonist. However, I have my plate full for months ahead. I hope somepony else takes this.

3294777 Or some-/drake/gryphon/zebra/changeling/buffelo/minotaur/goat/breezy/alicorn/crystalpony and anyone I forgotten