The Crystal Empire has returned, and Princess Celestia has given Twilight Sparkle an important task: to save the Crystal Empire. Along with her friends, they try to recreate the Crystal Fair that had lifted the spirits of the Crystal ponies so long ago. But when she finds the Crystal Heart, King Sombra's magic traps her at the top of the castle, and instead of realizing Spike can help, she gets too caught up trying to escape. The Crystal Heart is hidden once again, and Sombra has captured Twilight and Spike. Sombra's army grows, and the whole of Equestria must stand together to battle this ancient evil.

Basically, I like the Crystal War segment of the Season 5 finale so much, I created an AU.