Finn Sword

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. In "I Am a Sword," it was lost until being found by Bandit Princess, who used it to steal gold and kill people. Finn accidentally stabs the Finn Sword with the Grass Sword, rendering it inactive. In "Reboot " the grass sword once again, touches the Finn Sword. This results in creating a strange grass humanoid. Due to having Finn's memories he later takes on the name and personality of Finn but starts to become a different person being known as Fern. Fern was killed (shattered into grass pieces) in "Three Buckets", this could mean that the Finn Sword is gone for good.

Abilities
The sword is first used in "Dentist" and is shown to have Finn's dream world duplicate trapped inside of it and able to speak directly to Finn from the blue sphere it is encased in. In "Crossover" it is shown that other characters besides Finn are able to hear Finn Sword's voice. Also, while Finn is using this sword in battle, his physical attributes are double what they are without it. This is more than likely linked to the dream world duplicate inside it.

Gallery
Espada Finn Finn Sword