Main story arcs for this season include Bubblegum adjusting to life in exile and eventually reclaiming the Candy Kingdom crown, and Marceline coming to terms with her vampiric nature.
Under orders from the King of Ooo, Finn and Jake discover one of Ooo's greatest secrets.
Bubblegum turns to Marceline for help when something threatens the citizens of her homestead.
The arrival of a visitor causes Cherry Cream Soda's life to fall flat.
The loyalty of Finn and Jake comes into question when the King of Ooo orders them to intercept a flying mushroom.
BMO and Football decide upon a deal, but one of them cannot keep up their end of the bargain.
Finn and Jake hunt a shadowy predator and Marceline asks Princess Bubblegum for a favor.
Marceline looks back on her life on her last day.
Old foes surface from Marceline's past.
An old adversary targets the Ice Kingdom and Marceline has to save Simon.
The gang search for Vamps.
Princess Bubblegum searches for a cure for Marceline and Finn and Jake battle a vamp.
Marceline's archenemy visits and makes an odd proposal right before battle.
The final confrontation begins.
It's BMO's birthday, and he gets to have his creator MO pay him a visit. Mo gives BMO a solo quest to go the factory and back.
BMO learns that all the others MO have been merged into 1 giant being, and of the brother he never knew he had.
Viola tries to get a part in LSP's play, but gets made into LSP's personal assistant instead.
BMO convinces his friends to join him in a live action cowboy role-playing game.
Finn and Jake attempt to track down President Porpoise before Vice President Blowfish takes over.
One very spooky night, Finn and Jake come face-to-face with an urban myth.
Finn, Jake, LSP and BMO seek shelter as they contend with some deadly weather.
Ice King suffers a heartbreaking loss and it's up to Finn and Jake to find the culprit.
Finn takes a group of at-risk Candy Kingdom youth on a camping trip they'll never forget.
Finn and Jake crossover into Farmworld Finn's dimension.
Trapped and alone, Finn must unravel the riddle of the weird cave with no exit.
Finn has secret meetings with a powerful wizard.
Finn and Jake infiltrate the Banana Guard ranks and stumble upon a conspiracy.