The Witch and the Hundred Knight: Revival Edition

Fed up with being unable to travel beyond the borders of her swamp, the witch Metallia forges a contact with the legendary Hundred Knight to help her realize her ambition of spreading her swamp throughout all of Medea. As the Hundred Knight, destroy Pillars built to prevent her swamp from spreading, and wreak indiscriminate havoc. However, in the back of your inhuman mind, you begin to wonder. What prevents Metallia from leaving the swamp? Why do the other witches shun her, and how can she survive in a swamp that is notorious for how poisonous its fumes are? Is Metallia really a witch to respect, or is she one to fear?