While exploring a secluded area at the behest of the King of Ooo, Finn and Jake come upon a Candy Dragon, but the greediness of the King of Ooo causes him to run away, whereupon Finn and Jake seek Princess Bubblegum's help to solve the problem.
As Marceline comes to the Candy Kingdom, she's taken aback when she learns that Bubblegum has been dethroned, whereupon she helps her ward off some pesky varmints.
After Cherry Cream Soda marries Starchy and tries to move on with her life following the death of her former husband, Root Beer Guy, the latter suddenly comes back to life, leading to drastic consequences.
When the King of Ooo charges Finn and Jake with finding a flying mushroom for him to ride, the duo embarks on a wild adventure to carry out his orders.
BMO agrees with Football to swap places for a day, after which Football refuses to go back to the mirror world and decides to stay in the real one, so BMO tries to find a way out of this pickle.
As Marceline doesn't want to be a vampire anymore, she asks Princess Bubblegum to help cure her vampirism, but things take an unexpected turn when the vampiric essence taken out of Marceline's body turns into a vampire and runs away.
Left to be killed by the rising sun, Marceline gets flashbacks of her former life up to her encounter with the Vampire King, while Jake meets the vampires, whom Marceline slew in the past, after they have been brought back to life by the vampiric essence.
As five baleful vampires wreak havoc on the land of Ooo, Marceline recalls the time when the Vampire King bit her, killing himself in the process, after which she sets out to put an end to their menace.
Upon her arrival in the Ice Kingdom, the Empress hypnotizes the Ice King to do her bidding. After he captures Finn, Marceline manages to free him but is overpowered by the Empress, whereupon Bubblegum comes to her aid.
Marceline and the group take on the Hierophant, a powerful, shape-shifting vampire with a fatal weakness, which they use to their advantage.
After having poisoned by the Hierophant's stinger, Marceline is taken to the Candy Kingdom, where Princess Bubblegum tries to find her the antidote, while Finn and Jake attempt to track down the Moon, whose healing powers might be Marceline's last hope for survival.
The group receives an unexpected visit from the Vampire King, who drops a bombshell on them, declaring that he no longer wants to be a vampire, but after Bubblegum extracts his vampiric essence, trouble ensues.
As the Dark Cloud attacks the Candy Kingdom, Finn, Jake, and Princess Bubblegum stand up to it, prompting the people of the Candy Kingdom to depose the King of Ooo and join them, whereupon the dejected Marceline is inspired to fulfill her destiny and destroy the Dark Cloud.
It's the birthday of BMO, who receives a visit from Moe. As Moe sends BMO on an important mission, the former starts enjoying his stay at the treehouse a bit too much.
While at the MO factory, BMO makes some startling revelations about the guest at the treehouse, whereupon dire consequences occur after BMO returns home.
With LSP directing a play, Jake's daughter, Viola, wants to play the lead role, but LSP puts her in charge of sound and practical effects; however, a surprising turn of events takes place on opening night.
BMO organizes a live-action, role-playing game that involves a bounty. As Jake agrees to play the role of BMO's horse, they set out to catch Finn, who agrees to play the role of a notorious outlaw; however, things don't go as planned.
As Finn and Jake discover that President Porpoise is missing, they set out to look for him, enlisting Banana Man's help in the process.
Finn and Jake freak out as news spreads of a mysterious creature, the Blank-Eyed Girl, frightening the residents of Candy Kingdom by staring creepily at them.
With a storm in the offing, Finn, Jake, LSP, and BMO decide to construct a bunker, whereupon each one sets out to gather some of the things they're going to need during the storm.
After the Ice King's crown and Gunter the penguin go missing, the former asks Finn and Jake to help him find them, leading to an extraordinary adventure.
In the hope of reforming a bunch of at-risk Candy Kingdom youngsters, Finn takes them on a camping trip that turns out to be unforgettable.
Finn and Jake embark on a perilous mission to Farmworld, an alternate dimension, in an attempt to prevent another version of Finn as well as a familiar villain from undertaking a fateful action with disastrous consequences.
Finn finds himself trapped in a bizarre dungeon, from which he tries to escape, but it proves more difficult of a challenge than he'd thought.
As Jake has a sneaking suspicion that Finn likes Huntress Wizard, he tries to get him to confide in him, but Finn insists that it isn't true; however, an unforeseen chain of events proves otherwise.
Princess Bubblegum tasks Finn and Jake with infiltrating the ranks of the Banana Guards and finding out which one of them is responsible for creating murals on public property.