"Well... okay, the Elements respond to disharmony by introducing some sort of harmony back into the equation," Twilight said, and Erin recognized that 'lecture mode' was in the process of activating. "The effect varies depending on the nature of the disharmony, and the strength and nature of the wielders. For example, with Nightmare Moon, when Celestia wielded them, she was only able to banish her to the moon. Which doesn't mean Celestia is weak!" Twilight added quickly, looking up at Erin as if daring her to disagree. 