Strange discovers that the Ancient One, who strictly forbids her students from tapping into the Dark Dimension, has been drawing dark energy from Dormammu for centuries to maintain her immortality and protect Earth. This revelation shatters Mordo’s faith and validates Kaecilius’s claims of hypocrisy.
During a confrontation at the New York Sanctum, Kaecilius mortally wounds the Ancient One. Strange projects his astral form alongside hers as her physical body undergoes emergency surgery. She extends the final millisecond of her life, revealing that she has foreseen all possible futures up to this exact moment, and that Strange’s willingness to break rules is what makes him necessary.
In Hong Kong, Kaecilius completes the destruction of the Sanctum, causing the Dark Dimension to consume Earth. Strange uses the Eye of Agamotto to rewind time, reconstructing the city while fighting in reverse. Flying into the Dark Dimension, Strange confronts Dormammu directly. Because the Dark Dimension is a realm beyond time, Dormammu is utterly unfamiliar with temporal mechanics. Strange uses the Time Stone to cast a loop: every time Dormammu annihilates Strange, time resets to the exact moment Strange says, "Dormammu, I’ve come to bargain". Strange accepts being murdered thousands of times in excruciating ways, trapping Dormammu in an inescapable cage of time until the demon surrenders, banishing Kaecilius and sparing Earth.
Strange defeats the cosmic threat not by overpowering it, but through infinite self-sacrifice and weaponizing mortality itself against a timeless being. Disgusted by Strange and the Ancient One's reckless manipulation of natural laws, Mordo abandons the order. In the post-credits scene, Mordo visits Jonathan Pangborn, strips him of his magical mobility, and declares his new mission: Earth has "too many sorcerers".