The Finn Sword is created in 'Is That You?' after Finn sacrifices an alternate version of himself to save Prismo. After visiting a much more elaborate version of Prismo's Time room, created as a 'Plan B,' Finn makes a choice to save Prismo by creating a paradox that vaporizes his dream world duplicate. Instead of turning to dust, Finn's body turns into a sword, dubbed the Finn Sword by Prismo. The Finn Sword first appears in 'Breezy' when Finn awakens to Breezy's final song. However, instead of seeing Breezy in her Queen form, he has a vision of Princess Bubblegum holding the Finn Sword.