In my story 'Journey to Midnight Castle', I planned for Twilight to become an Archmage in the Coronation. Basically, every four years, Princess Celestia chooses one of her most promising students to become an Archmage, but I need ideas on how to make the Archmage more powerful than a normal mage.

Edit: By the way, the Coronation takes place in Chapter 1, before Nightmare Moon returns to Equestria.