The penultimate episode of Fionna and Cake Season 2, “The Worm and His Orchard,” arrived with a harvest of long-awaited answers and resolved several mysteries established earlier in the season. Yet, for veteran Adventure Time enthusiasts, the most electrifying moment was the reappearance of a fan-favorite character. For those who didn’t navigate all 283 episodes of the original run or whose memories of the 2018 finale have faded, this cameo might feel a bit enigmatic. Here is a comprehensive look at the lore behind this return and how the spin-off is finally weaving together a narrative thread left dangling for years.
[Editor’s note: The following contains significant spoilers for Fionna and Cake Season 2, Episode 9.]The Botanical Doppelganger: Fern’s Long Road to the Undergrowth
Upon her arrival in the Undergrowth, Fionna is promptly ensnared by predatory flora, only to be liberated by Fern, Finn’s long-lost grass-based counterpart. While Fionna’s home dimension features its own version of the character named Fennel, this encounter represents the first time the primary Fern has appeared since the Adventure Time series finale. When questioned about his identity, Fern reflects on his existential shift: “I remember sort of dying in Ooo, but my consciousness awoke here. I tried to be Finn… but I’m something else now.”
To truly grasp Fern’s significance, one must revisit the saga of Finn’s legendary armaments: The Grass Sword and the Finn Sword. The Grass Sword debuted in Season 5, a cursed blade Finn acquired from the Grass Wizard. Though intended to bond with its owner eternally, Finn eventually learned to harmonize with the weapon’s volatile nature. However, the sword remained a reactive force, leading to the traumatic loss of Finn’s arm during the “Escape from the Citadel” arc, where the blade transformed into a violent vine that severed his limb.
Image: Cartoon Network
Following a period of healing, Finn’s limb regenerated, housing the Grass Sword as a thorn in his palm. Concurrently, the “Finn Sword” emerged from a temporal paradox involving Prismo. This sword literally contained a version of Finn’s own soul. In Season 8, the two weapons were forcibly merged after the Grass Sword shattered the Finn Sword’s crystal core. This synthesis eventually gave birth to Fern, a being who possessed Finn’s memories and soul, but was physically composed of magical greenery.
Image: Cartoon Network
A Hero’s Shadow: The Tragic Mutation of Fern
Fern’s existence was plagued by the Grass Demon—an insidious entity that corrupted his psyche from within. This internal darkness transformed Fern from a confused ally into a bitter rival. His descent culminated in a lethal confrontation where Finn accidentally shredded Fern using his prosthetic arm’s “weed whacker” function. Although Fern was later resurrected by the villainous Uncle Gumbald as the “Green Knight,” he finally found redemption during the series finale’s dream-sequence battle. By slaying the Grass Demon within his mind, Fern was liberated, though he lost his physical cohesion in the process, leaving behind a seedling that Finn planted at their home.
Image: Cartoon Network
Healing in the Undergrowth: Finality for a Complex Soul
This history sets the stage for Fern’s peaceful return in Fionna and Cake. We now understand that upon his departure from Ooo’s physical realm, his essence was drawn to the Undergrowth—a metaphysical space defined by “green magic.” As a being born of botanical sorcery, Fern is a natural fit for this environment, which serves as a cosmic purgatory where trauma is processed and repurposed.
In this realm, Fern acts as a gardener of sorts, tending to “trauma trees” that manifest the psychological scars of the living. He even looks over Finn’s own burdened memories, including the heavy grief surrounding Jake’s passing (previously explored in the Distant Lands — Together Again special). Fern appears far more centered now, suggesting that his time in the Undergrowth has allowed him to transcend his former identity crisis. Whether this is a one-time cameo or a recurring role, seeing Fern find purpose provides a much-needed sense of resolution for one of the franchise’s most tragic figures.
Fionna and Cake is currently available for streaming on Max.
Source: Polygon
