- The "Tree Trunks" episode ends with the eponymous guest character taking a bite from the fruit they've been pursuing all episode. She explodes. Then we see her running, laughing, through crystal. Fortunately, that one got a Mind Screwdriver in "Crystals Have Power".
- Mixed with No Ending in "Evicted!". After a whole episode of dealing with Marceline taking over Finn and Jake's house, she gives it back... and they return to find a giant worm that blasts them with a ray of some sort and asks them to hug it. It got a Mind Screwdriver of sorts in "King Worm"... three seasons later! (And it also had an ambiguous ending, since it mirrored the final scene from "Evicted!".)
- At the end of "Power Animal", Jake suddenly says "Let's go eat Cinnamon Bun!"
- There was another one in "The Chamber of Frozen Blades" when Gunter, one of the Ice King's penguins that he took to the hospital, lays an egg that hatches... into a floating, pink cat. Then the Ice King says, "Gunter, why didn't you tell me?" (Gunter says "Wa-wa-wa" as if to say "I don't know") "Oh-ho-ho, Gunter-" as he is interrupted by Finn and Jake both kicking him. (While the cat would appear in later episodes, and it's revealed that Gunther is an Eldritch Abomination that existed for eons and was banished to Earth and trapped in the body of a penguin, but still no proper explanation for the cat).
- The end of "Her Parents" when Finn and Jake taste "Soy People," which is said to taste exactly like humans... of which Finn is the last. Not at all helped by Jake actually saying, "Finn, you taste delicious!". Then Finn tastes it and grins as the background music slowly tenses and gets louder, to the point where it gets distorted enough to blow out a speaker.
- In "The Other Tarts," the psychotic Tart Toter bursts into the castle, brandishing a chicken and a squirrel in place of tarts, foaming at the mouth. He says: "This cosmic dance bursting with decadence and withheld permissions twists all our arms collectively, but... If sweetness can win, (and it can!), then I'll still be here tomorrow to high-five you, yesterday, my friends. Peace." As he says this, the camera zooms in on his deranged, foaming face, and fades to the Tart Toter's delusion of drifting through space, surrounded by sweets, and LSP is in the space background, taking a donut. All of a sudden, it cuts back to the castle, where Finn cringes and says "Geesh...", and the episode ends.
- "Guardians of Sunshine" randomly ends with a "Game Over" screen. Note that Finn and Jake had already escaped from the video game by that point.
- "Vault of Bones" ends with Flame Princess finally managing to open the treasure chest that she and Finn have been trying to get into for most of the episode. It contains a green living creature that looks like a pair of buttocks, which winks at her. End credits.
- "Princess Potluck" ends with Jake getting randomly shot at the back of his head with an arrow by the squirrel from "The Duke", who has suffered, pardon the understatement, massive Sanity Slippage.Squirrel: YOU SON OF A BLEEBLOB! JAAAAAAAAAAAAAAAAAAAAAKE!!!
Jake: (not recognizing the squirrel) Heey... yooooou.
- "Shh!" abruptly ends with a Dance Party Ending... and then Party God (yet another Call-Back, this time to "Power Animal") comes in and crashes it.
- "The New Frontier" ends with Finn pretending to be a ghost while chasing Jake around the cave, and right afterwards comes a short sequence containing Banana Man doing a dance against a multicolored background. Note that before the sequence began, Banana Man was shown passed out in the pool.
- "Hug Wolf" ends with Finn managing to defeat the Alpha Hug Wolf who turns back into a female humanoid. Jake asks her for a hug, to which she suddenly turns into the tree monster from earlier. Cue Jake screaming, cut to black.
- "Box Prince". Finn gazes at the remains of the "kingdom" with the cats playing around and wonders if it even was a kingdom. The cats then dog-pile on Finn and purr. The end.
- "Breezy" ends with Finn and Breezy singing together about their love, which somehow causes the flower where Finn's arm used to be turn into a tree and explode, inexplicably regenerating his arm in the process. Then the episode suddenly ends without Finn and Breezy's relationship being resolved.
- Despite Finn's hand being restored and his vision never actually explained, his relationship with Breezy is resolved because she was in love with the flower on his hand, and not him. After Finn and the flower are separated, she stops having any interest in him.
- Another weird thing about this episode's ending is that immediately before this, it is strongly implied that Finn had sex with Lumpy Space Princess. They may have just been kissing, but it's ambiguous.
- "Mama Said" ends with three Banana Guards knocking the King of Ooo unconscious by pushing him down a flight of stairs while he sits on a pizza that he believes may be able to fly. The guards then awkwardly break into the song "Mama Said" by The Shirelles, for some reason.
- The ending of "Blank-Eyed Girl", where the six Blank-Eyed Girls reveal that their huge blank eyes are just giant contact lenses and they had normal eyes underneath, then they reveal that their hair isn't real, and then they unscrew their heads and shed their bodies, revealing them to be featureless, star-shaped beings who leave Finn and Jake's house through the window and break up into dandelion seeds. Finn and Jake are completely baffled, while BMO finds it beautiful.
Gainax Ending / Adventure Time