Ice King, NEPTR, Tree Trunks, Shelby, and Lemongrab are trapped inside a mysterious dungeon and must work together to free themselves.
Tropes
- Accidental Misnaming: Tree Trunks calls NEPTR, Ice King and Lemongrab "Nectar", "Ice Cream", and "Lemoncarb".
- Ascended Extra: Shelby has a major role in this episode.
- Bait-and-Switch: Shelby seems like he's going to perform a Heroic Sacrifice to kill the fish monster by serving as bait... but he instead uses Tree Trunks as bait.
- Beware the Nice Ones: It's Tree Trunks who ultimately gets them out of the dungeon, and she is one of the few people to get Lemongrab to behave himself.
- The Big Guy: Lemongrab instantly attacks and destroys the tentacle monster.
- Bowdlerise: Some versions of the episode cut Lemongrab eating pie from the giant rat's mouth. (Causing a continuity problem, as you can still see pie smeared around his mouth afterwards.)
- Combat Tentacles: The three-eyed monster has these for limbs.
- Cross-Referenced Titles: To Mystery Train.
- A Day in the Limelight: For Ice King, NEPTR, Tree Trunks, Shelby, and Lemongrab.
- Descending Ceiling: Both this and The Walls Are Closing In are used to force the five to leave the first room.
- Exact Words: Ice King throws the book containing his Fionna and Cake fanfiction into a magical fire since it is said that anything thrown into the fire can be brought to life. However, only the book itself is brought to life, much to Ice King's dismay.
- Formula-Breaking Episode: There's no Finn and Jake in this episode (until the very end, at least), but rather a group of people that you'd never expect to be in the same place.
- Gasshole: After being brought to life, the book of fanficiton repeatedly farts on Ice King.
- I'm a Humanitarian: Lemongrab is shown on several occasions to be cannibalistic, especially towards Ice King.
- Jabba Table Manners: Lemongrab's animalistic chomping notwithstanding, he eats half-chewed apple pie from the giant rat's mouth.
- The Lancer: Tree Trunks, of all characters, fulfills this role in this episode. She gets tough with Lemongrab and is surprisingly courageous and violent in the bit with the giant fish.
- The Leader: Ice King immediately takes charge.
- Literal Genie: The Sleeping Magi brings the book of Fionna and Cake to life and not the characters themselves.
- The Load: Shelby doesn't really do much. He was supposed to serve as bait for the fish monster but got Tree Trunks to do it instead.
- Mistaken Identity: The only reason NEPTR was in the dungeon was because Ice King thought he was BMO.
- More Teeth than the Osmond Family: Lemongrab has rows of razor-sharp teeth.
- Only Sane Man: Shelby spends the vast majority of the episode bitterly snarking at the insanity of their situation.
- Photographic Memory: Lemongrab is capable of memorizing the dungeon map in a few seconds before the ceiling starts collapsing.
- Plot Tailored to the Party: Invoked by Ice King. He knocks out and brings together the other four members because of their specific aptitudes. Tree Trunk's baking skills are needed in the second room of the dungeon to lure out the rat and, thus, uncover the trapdoor. Shelby, as a worm, is meant to be used as bait for the monster fish in the third room — he convinces Tree Trunks to do it instead, though. Lemongrab's lemon juice essence is the Weaksauce Weakness of the Tentacle Monster, who promptly explodes after squishing Lemongrab. Finally, BMO is an anthropomorphized gaming console so he could easily hack the mainframe of the central and last room's door. However, Ice King grabbed NEPTR instead. NEPTR is still able to fulfill the role by throwing a pie at the door, therefore short-circuiting it. Ice King's exact role remains unclear, but he still helps get them all through the dungeon by using his robe as a makeshift parachute.
- Ragtag Bunch of Misfits: Ice King is a loony ice wizard prone to kidnap princesses. Tree Trunks is a miniature, yellow elephant that bakes exquisite apple pies and is in love with a pig. Shelby is a worm that spends most of his time hanging out inside a dog's viola. NEPTR is a makeshift robot made of a microwave and a can, designed to produce pies out of nothingness, and given life by Ice King's magical lightning. And Lemongrab is Princess Bubblegum's failed attempt at creating sentient life, is literally made of lemon matter, and has a temper as sour as his namesake. Very misfitting, indeed, especially considering Ice King forgot NEPTR was his (kind of) son.
- Rhetorical Question Blunder: Upon seeing the very weird interaction between NEPTR and Ice King in which the latter was imagining NEPTR to be Fionna, Finn and Shelby have this exchange:
Finn: (ruefully) Who in this world is sadder than the Ice King?
Shelby: (snarky) Me, watching this.
- Rodents of Unusual Size: Tree Trunks' apple pie lures in a giant rat from a hidden door in the ground.
- "Shaggy Dog" Story: The Ice King had kidnapped everyone so he could try to bring his Fionna and Cake fanfiction to life. He throws in his book of fanfiction... and only the book is brought to life.
- Shout-Out:
- invoked According to Word of God, the episode's concept was inspired by the Cube films — Just like in Cube, "Mystery Dungeon" follows a group of people who wake up in a maze not knowing how they got there. Every room of the maze has a trap and is connected to other rooms, and the group must work together to escape.
- NEPTR's reference to the "garden of your mind" is a quotation from Mister Rogers' Neighborhood.
- The limbs and voice of the animated book are similar to those of Mickey Mouse.
- The Smart Guy: Ice King intended for BMO to play this role, but accidentally grabbed NEPTR instead.
- Stealth Pun: A literal Bait-and-Switch is pulled by Shelby having Tree Trunks used as bait to capture the fish monster instead of himself.
- Swallowed Whole: The giant fish monster doesn't even chew Tree Trunks when the party offers her as bait to it. That's why she's later able to emerge unblemished.
- Weaksauce Weakness:
- The Tentacle Monster's weakness is lemon juice, which Lemongrab has in spades when squished.
- Ice King's powers are useless in a warm and humid atmosphere.
- "Well Done, Son" Guy: Ice King to NEPTR.
Ice King: (hugging NEPTR) Oh-ho, my son! The grand prize of me loins!
- You Wake Up in a Room: The episode's opening has the five wake up in the dungeon with no memory of how they got there.
