Title: Avatar: Book of Harmony

Main characters: Mane Six, Spike, and the Gaang.

Genre: Crossover, Alternate Universe, Comedy, & Adventure.

Crossover With: Avatar: The Last Airbender

Cannon Placement:
MLP: After Equestria Girls.
Avatar: During Winter Solstice.

Premise:
While studying the Mirror Portal, Twilight attempts to cast a spell to help her see into other worlds through the mirror. It works briefly, but a mystic voice calls for her help, stating that a dark power has been spreading across their world.

At first, she spends her time studying the mirror and performing the same spells in an attempt to link herself to the other world, however her friend attempt to help her as well by suggesting they use Element’s. While Celestia is uncertain, Twilight reminds her that another world may need their help.

While they use the Element’s, the portal reacts negatively to their magic and ends up warping them all into an alternate dimension…the Spirit World, where they are separated and scattered throughout the new world.

Twilight & Spike travel through this new world until they come across an angered spirit that has taken a human hostage. Twilight attacks it, but it easily defeats her, however they are saved by another human named Aang, who arrives with another dragon and managed to quell the spirit.

After the introductions, the dragon reveals that her friends are safe, but have been flung out of the Spirit world and scattered throughout the nations, they must now find them all before the Fire nation does...