Rainbow Dash wants to write a rap. Somehow this leads to Sunset Shimmer explaining how magic in Equestria works.

Warning: Contains rapping, logic, and stupid headcanon

Princess Luna left some things in the moon when she returned after her thousand year banishment. To recover these forgotten items, the Lunar Recovery Program was created. But on the first launch, something goes wrong. The controls break and the crew finds themselves on a planet inhabited by an advanced bipedal species.