Universal Recreation

The "Universal Recreation" was an age-old prophecy that foretold a supernatural upheavel, in which the universe would be destroyed and recreated once the Slayer changed everything in the world.

Current events
This prophecy was apparently set in motion when Buffy Summers and the Scooby Gang cast a spell to activate all Potential Slayers at once in order to defeat the First Evil and its army of Turok-Han at the Battle at the Hellmouth ("Chosen").

The upheavel seemingly began after the Fall of Los Angeles, in which the vampire Angel gained the power to regenerate lost limbs after his hands and feet were ripped off in a battle with James. Polymephus revealed that this was due to an upcoming supernatural event ("Connorland").

The prophecy eventually came to pass when Buffy and Angel, the selected catalysts for the change, gained upgrades to their existing powers, including invulnerability, telescopic vision, and the power to fly. After a moment of passionate airborne sex, the two were transported to a pocket dimension while numerous hordes of extra-dimensional demons were unleashed upon the Earth to destroy it and allow the passage of the new universe. Though Angel initially planned to go along with the prophecy, Buffy realized the dire situation her friends were in, and the two ultimately decided not to abandon the paradise and destroy the demonic hoards.