Season synopsis
Contains spoilers for this season and earlier seasons.
Finn, Jake and BMO return from the human islands, but a mysterious orb interrupts their trip home with linked nightmares and hints that Ooo has changed. The change is the work of Patience St. Pim, whose elemental magic has transformed the land and many of its people into candy, ice, slime and fire. Finn and Jake join Ice King, Betty and Lumpy Space Princess to undo the disaster. They collect jewels from the elemental crowns for Betty’s plan to reset the world, but she pursues her own attempt to restore Simon and is sent to Mars when Ice King disrupts the spell. Lumpy Space Princess’s immunity lets her restore Ooo; Jake emerges in a blue, five-eyed form, but later returns to normal after visiting Jermaine.
The season also follows Fern’s growing frustration at living as a copy of Finn. In “Whispers,” Finn and Fern encounter the Lich’s severed hand, which Sweet P ultimately destroys, while Fern discovers he can disguise himself as Finn. Fern later invites Finn to explore old ruins, traps him behind a stone door and says he plans to replace him. Finn uses hidden tools in his mechanical arm to escape, and during their fight the arm’s weed-whacker setting tears Fern apart. Finn returns home shaken. Bubblegum’s Uncle Gumbald collects Fern’s still-living grass remains in a bucket, while Jake and BMO comfort the traumatized Finn.