With the demon sword now broken, Finn and Jake go shopping for a new one and come across a grass merchant who sells them a grass sword. However, the sword turns out to be cursed and is not willing to let Finn abandon it.
Tropes
- Absurdly Sharp Blade: Though it's made of grass, the blade can pretty much cut anything.
- Ambiguously Human: The pink/purple haired men that Finn and Jake fight at the beginning of the episode.
- Botanical Abomination: The last grass monster Finn confronts on the path to the grass wizard. It has the appearance of a giant tardigrade, with a retractable tubular mouth and several arms.
- Call-Back: Finn tries to find a new sword after the demon sword broke in "The Pit".
- The Cameo: Choose Goose makes an appearance.
- Clingy MacGuffin: The Grass Sword attaches itself to Finn's arm, and somehow gets back to the Tree Fort after Finn throws it in a river.
- Continuity Nod:
- Tree Trunks still bears her wedding ring.
- The lady armor that Choose Goose told Finn to wear in "Blood Under The Skin" appears.
- Cool Sword: The Grass Blade all the way, which is why Finn decides he's cool being stuck with it forever.
- The Cuckoolander Was Right: Tree Trunks thinks the sword is cursed after Finn cuts an apple far too perfectly. Finn and Jake don't listen, but she turns out to be right.
- Cursed with Awesome: Finn ultimately decides to keep the sword after coming to this conclusion, after it becomes permanently attached to his arm.
- Empathic Weapon: The sword refuses to leave Finn's side following it to bed and even returning after Finn kicks it into a river. Once he accepts it, it becomes more manageable by spontaneously developing a compact form so it can remain on his person while allowing free use of both hands.
- Evil Sorcerer: The Grass Wizard gives out cursed objects made of grass seemingly for the hell of it. He's annoyed that Finn decides he likes his new sword instead of despairing at being stuck with it forever.
- Green Thumb: The Grass Wizard controls all things grass related.
- The Little Shop That Wasn't There Yesterday: The grass shop that Finn acquires the sword from. It's just a tent made from tall grass tied together, which would already be easy to move even without being controlled by a wizard in pop up bazaar.
- Ludicrous Mêlée Accuracy: The sword is enchanted to perfectly cut whatever Finn turns it on, something which disturbs Tree Trunks enough to (rightfully) call it cursed. A running gag are things being carved into perfect busts of Finn's head, with even the face and eye holes being separate pieces that fall away after a moment.
- Pun-Based Title: "Blade of Grass" can refer to a single leaf of grass, but here it refers to the Grass Sword, a literal blade of grass.
- Retractable Weapon: Once Finn expresses acceptance that the Grass Sword will be bonded to him forever, it suddenly collapses into a band around his wrist. He takes a moment exercising his new ability to extend and retract it at will, making him even happier with it.
- Shout-Out: The title card music sounds like "The Birdie Song".
- Visual Pun: The giant grass monster is based on a tardigrade, also known as a "moss bear".
