Discord's power was something that always frustrated Twilight. All that power, with no effort, no cost. So when Discord offers her a chance to learn his secrets, Twilight quickly agrees. Unfortunatly all things come with a price.
For centuries, the old races of Equus have slept, slumbering on and on for years on end. Now, at long last, they are being awakened. Beware, Equestria, the Age of Ponies has come to an end.
Right before the Elements struck, the Nightmare unleashed a spell out of desperation. A substitution spell. Otherwise known as the correct use of Kawarimi.