Fern Fern is an " Adventure Time " minifigure introduced in LEGO Dimensions in 2017 . Background . In " Two Swords , " it is revealed that Fern was created when Finn accidentally broke the Finn Sword with the Grass Sword while fighting Bandit Princess , during " I Am a Sword . " Some time later a spider - octopus - like Grass Demon interacted with the small Finn inside the sword . The Grass Demon wrapped the sword Finn in goo , forming a cocoon around him . At an unknown period of time later , the interior of the sword was filled with green cobwebs and the cocoon appeared hardened . Both the sword Finn and the Grass Demon expressed desire to get out . The Grass Demon told the sword Finn to let it to do the talking when they escape . Fern emerged in " Reboot " when the Grass Sword touched the Finn Sword again and began to cover it until Finn ' s arm detached from his body . When Fern first emerged he looked like a lump of grass with a face but then began to look a like Finn but made out of grass , even gaining the ability to speak . He then revealed that he believed that he was Finn , remembering everything Finn remembered . When he first saw the real Finn he thought he was a threat , believing that the real Finn was just someone trying to be like him . He than went to Jake and asked him to tell Finn who the " real Finn " is , to which Jake logically responded that Finn was the " real Finn . " This upset him , and became more upset when Finn and Jake began yelling at him calling him a demon . After this Fern went to Finn and Jake ' s tree fort ( believing it to be his home ) . He than walked in and said hello to BMO . Confused by this BMO ran into a hole where Fern won ' t find him . Fern was confused ( and kind of in denial ) . Fern started looking through a scrapbook of Finn and Jake ' s adventures admiring it . Later Fern was frustrated and confused and began to trash the Treehouse , scaring BMO even more . BMO immediately called Finn and Jake and the two came straight home . When they got back Jake was furious with Fern for scaring BMO and trashing their house , making Fern even more upset . Realizing the creature meant no harm , Finn offered him a Finn cake . Finn cakes are for " Finn only " so this made Fern felt more like himself . The group then went to bed and forgave one another for anything they may have done or said . In " Do No Harm , " Finn had to step out of Tree Fort to check on Susan , meaning Jake had to be alone with Fern much to his chagrin . Finn told Jake to pretend that Fern was him so and do " Finn stuff " with him . Jake made Fern meatloaf , which Fern tried to eat but learned his body was unable to consume food . This upset him since Fern still had memories of food and how it tasted . Fern was also unable to play the flute since he doesn ' t breathe . Jake then gave Fern the idea of going to an " evil dungeon to smash . Fern then took Jake to the Grassy Mountain where the Grassy Wizard lives . On their visit they fought grass monsters which made Fern happy , albeit a little more violent than Finn would . At the top of the mountain they saw the Grassy Wizard , whom recognized Fern , realizing he came from the Grass Sword causing Fern to realize that he , made him . Fern then proceeded to ask why he ( as the grass - sword ) existed , only to learn he only made the Grass blade because it sounded cool and was a play on words , with no real dark plan behind him . When the Grassy Wizard asked Fern to kill Jake he than punched the Grassy Wizard as hard as he could , knocking him out . At the end of the episode the Grassy Wizard was hospitalized and Fern was upset but Jake said he did the right thing . Finn met with the two and told Fern he did a good job ( Fern was not yet named so Finn called him " Grass me " while others mostly called him Grass Finn . ) Fern then realized that he is not Finn so he came up with a new name , Fern the Human . Fern stole Starchy ' s motorcycle and took off . In " The Invitation , " it is revealed that Fern lives on top of the Tree Fort roof . Finn was about to leave for his journey to the islands so he wanted Fern to fill in for him while he was gone . Fern was flattered by this but Finn told him to kill monsters his way . It is also revealed that Fern crashed Starchy ' s motorcycle as well . In " Whispers , " Fern begins to become even more jealous of Finn . In " Three Buckets , " Fern finds out that he can make himself look like Finn , then he traps Finn on the other side of a locked stone door and tells Finn that he was Finn for too long and that it was his turn . After Finn discovers that he can turn his metal arm into rock breaking device , he breaks down the door and turns on weed - whacker mode . He tackles Fern and they fight , until Finn accidentally cuts Fern to pieces . Essentially , Fern is dead , but a mysterious man picks up his remains and puts it in a bucket and walks off . Fern ' s eyeball moved implying that he can still be alive in a way .