Fionna, Cake and their friends attempt to fight off the Scarab in their world as Simon, trapped in a mind from Ooo's distant future, tries to figure out a way back to his body.
Tropes Include
- Aesop Amnesia: Discussed. During a therapy session with Minerva, Simon says that while he's currently content, he worries he'll repeat the same cycle of depression and obsession in the future. Minerva says it very well could go this way, but that it could still improve as time goes on.
- All Take and No Give: Through playing Casper and Nova, Simon comes to realize this was the case between him and Betty - even though he wasn't malicious or intentionally manipulative towards Betty, Simon wasn't as considerate towards her as he could've been, constantly shooting down her suggestions in favor of doing things his way, and because of her obsession with him, Betty was willing to go along with whatever he wanted to do, creating a cycle where she constantly sacrificed herself to support his dreams, rather than pursue any of her own. They genuinely loved each other and Betty harbors no regrets over it, but Simon is still left distraught over his self-centered actions, admitting he should've been more thoughtful and supported her in return. Meanwhile, the trope almost plays out with Simon on the giving side by turning back into the Ice King to turn Fionnaworld back to normal, but Betty helps him realize his life as Simon Petrikov does have value, and as such he instead throws the crown into the abyss.
- Ambiguous Situation: Simon isn't sure if he was really speaking to Betty in his mind or just imagined the entire conversation, as GOLBetty can't speak to confirm either way.
- Attack of the 50-Foot Whatever: Fionna consumes all of the magic strawberries that the Squirrel brought with him, causing her to become a Giant Woman to give her an advantage against Scarab.
- Bittersweet Ending: While definitely more on the sweet side, especially after everything the heroes had to go through, there are still some sad notes. Simon fails to reunite with GOLBetty, and they part ways for good after he realizes that their past relationship was inadvertently All Take and No Give, and Fionna and Cake fail to fully bring magic back to their world despite it becoming "canonized" and safe from Scarab's ravages.
- The Bus Came Back: When Simon is jumping on the different universes, one of them shows the Snail in a Freeze-Frame Bonus and another shows the Water Park from "Water Park Prank". Later on, during Simon's therapy session, a Minervabot is listening to and advising him.
- Call-Back: Fionna's world turning into a dandelion calls back to Hunter's view on weeds, where he sees them as plants rather than something to get rid of.
- In previous episodes, Fionna said that Cake talking and a kingdom made entirely of candy were each "one of [her] top 3 fantasies". Here, we get to see what her top fantasy is: becoming a giant.
- The Cavalry: To help Fionna and Cake fight against a rampaging Scarab, Prismo sends Baby Finn, the Peppermint Tank, the Squirrel, Jay Mertens and Little Destiny to their world to help out.
- Cryptic Conversation: GOLBetty's interactions with the Lich and Simon amount to this, as she can't speak and can only respond with actions, except for when she's speaking to Simon in his mind as her past self.
- Earn Your Happy Ending: Although Fionna and Cake don't get magic fully restored to their universe and GOLBetty and Simon end up splitting for good after realizing how their relationship was inadvertently All Take and No Give, the miniseries ultimately ends on a positive note. Fionna and Cake's world is out of Simon's head and officially part of the multiverse, keeping Scarab from erasing it, Simon is moving on and getting therapy, looking much happier when talking to Astrid about the past, and Baby Finn, Little Destiny, Jay, and the Squirrel have all moved to Fionna's world, which has rebuilt from the damage Scarab caused and is looking towards the future.
- Freeze-Frame Bonus: The universes Simon hops on as he return to Prime Ooo are only visible for a single frame. Among them are all the ones they've visited on their adventure (with the Winter Kingdom shown to have melted into a massive lake), the volcanic landscape of Evergreen (with the lava monster visible in the background), the water park from Water Park Prank, and what appears to be the Jake world from Everything's Jake.
- Hard Truth Aesop: Sometimes you have to accept the choices you made and move on.
- Life’s a cycle of learning and forgetting.
- Hoist by His Own Petard: Scarab’s comeuppance includes getting blasted and egged by his own crystal at the hands of Cake.
- Humongous-Headed Hammer: Cake morphs into a hammer to assist the magic strawberry enlarged Fionna, which she uses to reduce Scarab to a crippled state.
- I Choose to Stay: Jay and Little Destiny ask to stay in Fionnaworld, much to Cake's excitement and immediate agreement. In the montage sequence at the end, it's shown that The Squirrel, Kheirosiphon, Peppermint Tank and Baby Finn also stayed.
- Laser-Guided Karma: Scarab is punished for his transgressions by becoming a Living Shadow under the tutelage of Prismo in creating universes. That said, Prismo implies that this may lead to Scarab succeeding him as Wishmaster in a few centuries, which is still what he wanted anyway.
- Magic A Is Magic A: Fionna's world is basically one of Prismo's wishes. When it turns into a dandelion, and Simon gives it to her, Fionna blows to make a wish that makes it part of the multiverse.
- Morton's Fork: The bad ending of Casper and Nova forces Casper into either sacrificing Nova as a doorstep to reach the crown or using a potion that will make him strong enough to force the gate open, but forget about Nova forever in the process. Simon laments that there should have been more choices, but Beth replies that there could've been more if Simon hadn't always picked Casper's choices over Nova's.
- My God, What Have I Done?: After being confronted with a Morton's Fork while playing Casper and Nova, Simon realizes that he acted just like Casper (who, while not malicious, was so single-minded in reaching his goals that he never noticed that Nova was constantly sacrificing herself for him) during his relationship with Betty, admitting that he could've been more thoughtful and supported her the way she did for him.
- Shout-Out: Gary's response to Scarab emerging in Fionna's apartment: "Oh no, he's hot".
- During the fight against Scarab, Cake transforms herself to resemble Godzilla.
- Ship Tease:
- It's downplayed, but Fionna seems to click better with Hunter overall, and the two are tending to plants together in the final scene.
- It's extremely easy to miss, but DJ Flame and the female, human Fern can be seen holding hands.
- Sore Loser: With Fionna's universe being canonized, there's no longer any reward for Scarab if he destroyed it. Unfortunately, he attempts to destroy it anyway just because he wants to get back at Prismo for getting away with it.
- Stable Time Loop: It's implied that Astrid ends up creating the Casper and Nova hologram game based on Simon telling her about it, given that she's seen drawing the duo in her notebook.
- The Stinger: A very short one. After the credits, there's a depiction of a pale green cube and red pyramid fusing together into an apple with a white bow tied around it.
- The Un-Reveal: In the end, the identity of Prismo and/or the Scarab's boss is not revealed. Likely the setting's Top God.
- They're Called "Personal Issues" for a Reason: At the end, Simon begans to thinking about moving away from the museum after being annoyed at the museum's guests delighting in his therapy session with Minerva.
- Urban Fantasy: While Fionnaworld doesn't return to the more Ooo-inspired state it previously was, thanks to the Scarab's prisoners being freed within it and others from the multiverse being sent to it by Prismo, it becomes a small blend of fantasy and modern times. The general public appear to have embraced or at least accept magical beings like Cake and Scarab's freed former prisoners, which seems to already be causing a ripple effect.
- Villainous Breakdown: After Fionnaworld is canonized and being told off by his boss, Scarab completely loses it and starts destroying the city simply because he can.
- Wham Shot: Prismo's face is seen briefly glitching out while he's talking to Scarab during the epilogue, although whether or not this means something is wrong with him remains to be seen.
- "Where Are They Now?" Epilogue: After Scarab is defeated, we get a montage of how life progresses for many of the characters, set to the tune of "Blue Shift" by kendall :3.
- Fionna, Cake, Marshall Lee and Gary all work to rebuild and repair the destruction left by Scarab. Later, they all hang out together in the bakery, and Fionna helps Hunter replant flowers.
- Simon Petrikov, now having some closure with Betty, returns to Ooo and happily drinks with Dirt Beer Guy and T.V. He also keeps in contact with Fionna via phone and has made up with Astrid, and he later talks to a Minerva-Bot about moving out of his exhibit home.
- Gary starts selling his pastries in the back of Marshall Lee's van.
- Kheirosiphon gets a job as a waiter at the bakery.
- Marshall Lee, Ellis P. and a group of citizens stand outside of Hana Abadeer's home to protest for lower rent, which she simply ignores while drinking a glass of wine.
- Jay and Little Destiny go on a date at the aquarium, marveling at fish as they hold hands.
- Fionna has joined the Human Skater Fairies roller skating team and later helps Hunter plant Dandelions while Baby Finn and Peppermint Tank run through the field.
- Cake travels around the city with her stretching powers as everyone around her has gotten used to it while she greets the squirrel.
- Prismo whose face glitches for a second and a now-Living Shadow Scarab work together on Prismo's character creation program.
