"From Bad to Worse" is the thirteenth episode in the third season of Adventure Time. It's the sixty-fifth episode overall.
When another plague of Candy Zombies arises and Princess Bubblegum is among the undead, Finn and his friends are in a race against time to figure out how to stop it. but things get worse by the minute.
The episode begins with Finn, Jake, Lady Rainicorn, and Lumpy Space Princess racing through the Candy Kingdom, which has become overrun with bloodthirsty Candy Zombies. They just barely escape into the Castle, exhausted and worried that another zombie outbreak has overtaken the Candy Kingdom. They meet up with Princess Bubblegum and she explains how and why she is once again responsible for unleashing this nightmare onto her beloved kingdom. She was experimenting with a sample of candy zombie tissue she had saved from the last outbreak when Cinnamon Bun came into her lab looking for food. She turned her back on him for 5 seconds and he gobbled down the flesh in delight, which unbeknownst to him was highly contagious. By the time she realized her mistake, it was too late. She managed to escape, but she wasn't able to stop Cinnamon Bun from spreading the zombie contagion to the rest of the kingdom.
So now, because of her carelessness and his gluttony, they are surrounded by undead cannibalistic corporeal revenants. Luckily, she has all the notes she needs to get to work on the antidote formula and she comes prepared with hammers, nails, and plenty of wood to barricade the windows. Unfortunately, her carelessness once again proves to be her undoing when a candy zombie bursts through the unprotected window right behind her and bites her on the shoulder. Finn grabs her hands and holds onto her for dear life as she is dragged outside into the hoard. With last words as the zombie virus overtakes her, she tells Finn "Just Let Science do the work!" and she goes full zombie before she can specify. Horrified, Lumpy Space Princess then pushes Finn away from the window and hits zombie Princess Bubblegum with a board, and nails the board to the window, declaring that she is not getting eaten by zombies tonight. While Lumpy Space Princess fights off the zombies with her hammer, Finn is frozen with fear to see his beloved Princess zombified in front of his eyes. His moment of mourning is interrupted by Jake with Princess Bubblegum's notes, and he speaks for everyone when he says they are nothing but ghobbledy ghak to them. In light of this setback, Finn simply declares that each of them will have to make their own version of the formula with a 25% chance between them of coming up with the batch that saves the Candy Kingdom.
In Princess Bubblegum's laboratory, the 4 of them divide and conquer with one of the 4 pages of Bubblegum's notes for the formula. Doing the best they can to follow each of their respective pages, they combine all the random serums, compounds, and chemicals in all the vials, beakers, and tubes they can find trying to perfect each of their versions of the serum. While they work, they notice Princess Bubblegum's candy corn lab rat is dancing for them, which they understandably find amusing given the frankly nightmarish circumstances. They declare they're finished when each of the serums in their beakers erupts with fizz. When all of them come up with finished formulas, they move on to the testing phase.
The gang rushes back to a boarded-up window in the grand foyer with zombies trying to claw their way inside. Finn tests his serum first, but with horrible results. The candy zombie sprouts enormous, feathered wings and spreads the mutation to the rest of the zombies by biting them. The situation has gone from bad to worse now that the gang is surrounded by flying Candy Zombies that are now flying into the wooden boards trying to break through. On top of a building, Starchy is viewing the army of zombies on the ground and states he is glad he is not down there with all the zombies. He does a little dance, but his advantage is painfully short lived as he is snatched up by Pineapple Guy who can now fly with his wings and is thrown into the window and breaks through the wood. With the grand foyer breached, the gang escape to the top of the castle to continue to try and cure the zombies. From a furnace room high in the tower, Lumpy Space Princess drops her formula out the window onto the zombie hoard, and it does nothing but give them enlarged lips. Thankfully, it doesn't give the zombies any tactical advantage like Finn's did, but it does cost Lumpy Space Princess her own when she is so enamored by their newfound luscious lips that she rushes back downstairs to get some for herself. She goes outside and barges into the middle of the zombie hoard to lick up the rest of her formula. Her plan works (more or less due to her "lumpy" physiology), but she ends up getting completely surrounded and Finn, Jake, and Lady Rainicorn can do nothing but watch as Lumpy Space Princess is totally devoured by zombies. Things have graduated from worse to horrible now that another one of their friends is now an undead cannibalistic corporeal revenant with feathered wings and luscious red lips. With only one formula left, all they can do is pray the one Jake and Lady Rainicorn made will come through for them. Jake sprinkles it on the zombie hoard, but just like Finn's, it only mutates them with a tactical advantage in their favor. This formula increases the muscle mass in the zombies' arms exponentially, thereby only making the situation 10 times more horrible than it already was.
The candy zombies use their new abilities to break through the window in the top of the castle and surround the group. With only one hiding place left, they retreat back to the chemistry lab. They just barely arrive and lock the door behind them with the zombies trying to break it down. The door is made of candy steel, but it won't hold off those mutant super zombies forever. Just when they think they have a moment to reconvene, the zombie Candy Cane Guy comes out from the lockers and tries to sneak up on Lady Rainicorn. Jake shoves him face first back into the lockers, seals the doors, and then uses the lockers to barricade the door. Finn asks Jake if he got compromised but doesn't worry about the tiny bite mark on the palm of his hand. Unfortunately, that tiny bite proves to be enough for the virus to spread and Jake's entire hand is infected in seconds. Thankfully, Jake is able to use his Stretchy Powers to perpetually elongate his arm and prolong the effects by keeping the virus from reaching the rest of his body. Lady Rainicorn can clearly see Jake is in trouble, but Jake tells her he can keep this up forever. However, fearing the inevitable, Jake whispers to Finn to hurry up with the antidote. Jake is then literally on the run from his own arm trying to outstretch his zombie infection while Finn stresses trying to figure out where to begin. Jake then suggests turning to one of the books over by the lab rat and Finn finds a glossary of symbols. When he sees the rat continuing its bizarre dance routine, he tells Jake he believes the rat has "serious dance fever." Jake seals himself inside the science shower, telling Lady Rainicorn to keep her distance just in case, secretly knowing he's going to turn any second. Lady Rainicorn watches Jake keep up the effort in outstretching his infection in his cylindrical prison while he tells Finn to hurry up with the new decorpsinator batch. Finn keeps scrolling through the book while brewing the serum and doesn't stress because while he knows Jake is about to turn, he's finally getting somewhere with the antidote now that he actually has a way of reading Princess Bubblegum's notes. Lady Rainicorn loses contact with Jake and his arm retracts into the science shower until he reveals to her horror that her boyfriend is now a full-fledged zombie. Finn tells Lady Rainicorn to stay calm, informing her that he'll have the antidote ready soon. But for the time being, not to let Jake out, telling her that what she's looking at is no longer Jake. Lady Rainicorn feels sorry for him and lets Jake out anyway. They share a kiss, only for Lady Rainicorn to be bitten. Finn turns around to see in horror that two zombies are now loose in the laboratory. He runs for dear life with the science cart he is operating on and loads the lab rat's terrarium onto it. The candy zombies then finally break through to the lab, and Finn quickly locks himself in the science shower with the cart and the rat. He sits down with the rat only to realize he dropped the book outside and then looks up to see muscular fat-lipped zombies pounding on the glass standing between him and the book. Without the book to translate Princess Bubblegum's notes, Finn cannot finish brewing the antidote and all hope is lost. Now totally alone and completely trapped with no hope of completing the antidote, Finn can do nothing except apologize to everyone surrounding him that used to be his best friends in utter failure. With nobody else to talk to, he finds it funny he doesn't even know the rat's name. When she directs Finn's attention to the label on the corner of her terrarium, one that reads "Science TS 19-04", Finn realizes her name is Science. He then remembers when Princess Bubblegum said, "Just let Science do the work!" when she got zombified. That's when Finn figures it out: When she said, "Science. is. MUHRAAHH," she was attempting to say, "Science is my rat," when she got zombified. Finn then, in turn, realizes that Science was the key to ending this nightmare all along. He takes her out of her terrarium and lets her read Princess Bubblegum's notes. Science then puts on some music and gathers up all the correct ingredients that she has Finn brew in a beaker. Once they're all accumulated and mixed up, they finally have the antidote. Using a dropper, Finn sneaks a sample out through the top of the door and tests it on Jake. He reverts back as if he was never infected, proud of Finn to have succeeded. Unfortunately, the joy is short-lived when Jake is then bitten by the mob of Candy zombies that he was just part of, and he is instantly re-zombified. Science has no choice but to admit to Finn that the antidote is useless without some sort of wide-dispersal method, because the zombie plague will just start up again if so much as one zombie is allowed to remain. With the zombies breaking through the glass, Finn is struck with a disgusting idea. While he has Science duck for cover, he dumps the antidote onto his head, completely and quickly covering himself in it. The crowd of zombies break into the science shower and swarm him, gnawing on him and leaving Finn in indescribable horror.
As the sun rises, Finn's disgusting idea to use himself as bait to deliver the cure to the candy zombies has worked flawlessly. The Candy People, along with Jake, Lumpy Space Princess, and Lady Rainicorn, are back to normal, good as new as they enact the Royal Day of Apologizing. Princess Bubblegum proudly declares the time of apologizing is over and now is the time to celebrate the one who saved them all. She approaches Finn with the royal medal of heroic bravery and asks him to move out of the way. He complies and she presents the medal to Science, who Finn helped concoct the antidote that eradicated the zombie virus once and for all. With the power invested in them, the Candy Kingdom rejoices in honor of their hero, Science the Rat.
