[Rainbow's Crack in the Sky - http://www.fimfiction.net/story/10350/Elements-of-Harmony---Turn-it-Up]
In a world of flowing magic, a perfect 10 on the scale measuring magical performance starts tapping into the stream of flowing magic. But what IS this river of magic? And why does it flow so fast inside Twilight?
Following the pattern of Rainbow's discovery of her hidden powers, Twilight, with help from Celestia's lies, and one... peculiar relative of the princess, the unicorn joins Rainbow Dash on the quest to take the power of the Elements up another notch.