Worshiped: modern-day Arthurian urban fantasy

How can my magic defeat a goddess? I'm an immortal magician who only wants a peaceful life with his fiancée. My elemental nemesis was soundly beaten-so I thought-but now she's back and plans to reign over all humans in the guise of a resurrected Aztec deity. She will do anything to sway her followers. Every day, more people are drawn to her earth-worshiping cult at the cost of their lives. Can I stop this self-proclaimed goddess before the entire city is under her dominion? I am Merlin-but I need to be more.