A future crystal appears in the episode "Dungeon Train" and has the magical ability to let a person see their future by looking into it. It is gained on the Dungeon Train by a random monster as Jake peers into it and sees Finn's future - an old man with armor (and a prosthetic arm) continuing to fight monsters, but with a rather sad emotion. It is used again when Finn looks into it and sees an old Jake following Finn around the Dungeon Train. At the end of the episode, they both look into it after Finn has the will to leave the train, and they both appear in their house washing dishes together.
In "The Hall of Egress", Finn was forced to close his eyes due to the Hall of Egress. The Future Crystal shows Finn and Jake washing up and Finn has his eyes closed. This may have been a view into the distant future around 2 seasons away.
Bed cars •
Big Baby Root Beer •
BMO's Official Strategy Guide to Snake Eater •
Boats in the Clouds •
Bucket of Caramel •
Candy Bar Card Game •
Captain Tasty's Placemat •
Cold Fart •
Füt Stüff •
Lemonpink's carriage •
Magic Fertilizer •
Magic Key •
Marceline's puppets •
Mystic Soup •
Potato-head curse antidote •
Propeller beanie •
Skyhooks •
USB drive
Season 10
Birthday Boyfighter •
BMO and Ice King's valise •
Breakfast Porridge •
The Cake •
Danny's boat •
Der Witz Und Seine Beziehung Zum Unter Bewussten •
Device for the Dissolution of Invisible Shields •
Dum Dum Juice •
Elk's Heart •
Finn's Vault •
Green Knight's Axe •
Gumbald's baseball caps •
Gumbald's goblets •
Gunter's puppets •
Invisible Shield •
La Femme du la Mer •
Love Bazooka •
Mechanical horse •
Megaphone •
Memory drive rocket •
Mr. Cream Puff's car •
Night Sword •
The Panzark •
Peanut •
Personal hover-platform •
Power-siphoning belts •
Princess Bubblegum's laser weapon •
Sledgehammers •
Techno-harpoon •
Warren Ampersand's rocket
