Shapeshifting Powers (referred to on the show as Stretchy Powers) are the powers that Jake and Cake use to change the shape of their bodies. Jake has been seen to use a variety of Shapeshifting Powers.
Jake claims that he thought he might have gotten them by rolling around in a mud puddle when he was still a pup, as stated in the episode "The Witch's Garden," but Pendleton Ward stated on Spring that this wasn't how he got his powers and that Jake just couldn't remember; Jake doesn't know the full use of his powers because he was too lazy to use them fully until "The Limit."
Jake's powers were finally revealed to be hereditary in "Joshua and Margaret Investigations ," inherited from his biological "father," Warren Ampersand, who is from an alien world or dimension. The creature appeared to merge its DNA with Jake's father Joshua by biting him on the head, creating Jake. This proves that Jake's powers are a biological mutation and not magical in origin, as Princess Bubblegum stated in "Wizards Only, Fools."
Stretchy powers include stretching one body part at a time or change size and mass. Jake can be stretched by force as seen in "Ocean of Fear," where Finn stretched Jake's ears to avoid making contact with the ocean, and in "Beautopia," when Susan stretches him into an oar. It's also shown in "Hot to the Touch," where Finn was able to morph Jake's face around freely. It is also shown in "Burning Low," when Finn takes Jake's arm and stretches it down with him to get Flame Princess. Jake can also grow his entire body to accommodate multiple riders, as seen in "Prisoners of Love," and shrink so that Finn can hold him and fit in his pocket, as seen in "It Came from the Nightosphere" and "Goliad."
Jake's also been shown to completely morph the shape of his body into various other structures (in the episode "Loyalty to the King," Jake makes an ear shield so he and Finn can get by the princesses, and in "Return to the Nightosphere" he changes shape to resemble a demon), harden/sharpen parts of his body (Beautopia showed Jake transforming his hand into a pickaxe to pop one of the Lub Glubs' false pool-floaties), and many other general transformations that are usually applicable to the situation at hand. He can stretch into a car, as seen in "The Lich" and "Candy Streets."
In the episodes "Business Time" and "The Pods," it is shown that no matter how much Jake eats, he can still stretch back to normal size. Jake can also change the shape and quantity of his teeth, as shown in "Daddy's Little Monster" when he shape-changed into a demon.
In "Goliad," it is shown that he can forcibly expel people from his body by holding his breath and making them "pop" out of his body. It is also shown that he can repair the holes when he "pops" them out. This ability was also seen in "You Made Me" when Princess Bubblegum jumped into Jake's mouth and he moved her to his back.
Jake also seems to have an amount of control over his bodily functions, as he could transfer all his blood and internal organs into his thumb in "Evicted!" to prevent Marceline from sucking his blood. In "Jake vs. Me-Mow" he grew his liver 51 times its normal size to filter out the poison in his body which shows he can also control the size of a particular organ.
It is shown in "Two Swords" that Jake's body is very durable, capable of withstanding a anchor dropping down on him and recovering it from in mere minutes
Key Hand is a unique ability that is only known to be used by Jake. Key Hand consists of Jake morphing his hand into the shape of a skeleton key. Since Jake is a magical dog, he is the only known person in the Land of Ooo who can do this. This is very helpful when trying to open doors, prison cells, gates, and other obstacles that require the use of a key. Key Hand is first seen in the episode "Prisoners of Love." Jake attempts to use Key Hand to free all the princesses who were locked in Ice King's jail cell. Ice King realizes that Key Hand was a threat and quickly flash-freezes Jake. In the episode "Dungeon," Finn tries to use Key Hand to open a locked door, but without Jake's stretchy powers, he only hurts his fingers. When he is reunited with Jake, both are trapped in a cage by the Guardian Angel. Jake morphs his hand to make Key Hand; however, Finn doesn't see any locks. So Jake morphs his other hand into "Lock Hand." So far, Jake has been seen to use the Key Hand twice and failed.
In the game Legends of Ooo, Jake uses Key Hand so he and Finn could escape the ice dungeon after dressing up as a princess. This is the first time Jake is "seen" using Key Hand with any form of a successful result.
Jake Suit is an ability used for fighting evil that can only be done with the help of Finn. Jake transforms into a muscular guy and puts Finn in his mouth and his face sees out of it. Jake serves as the armor for Finn so he has control of Jake in there so he can do Jake's moves.
In the Adventure Time game "Finn and Jake's Epic Quest," this is used as a power-up in the game.
There is an upward limit to Jake's Stretchy Powers, for if he exerts himself too much he could die, as seen in "The Limit." This is because his body stretches like a piece of bubblegum, as the more he stretches, the thinner he gets, until it becomes difficult for his organs to function. In "From Bad to Worse," as he claims, Jake tells Lady Rainicorn he can stretch forever; however, he was likely lying to comfort Lady, since he whispers to Finn to "hurry up with that antidote."
As seen in "Jake the Dad," stretchy powers do not work as well when the user is tired.
- The name "stretchy powers" is technically a misnomer, as Jake is able to change the topology of his body (such as creating holes through his body), which would not be possible if his shapeshifting powers consisted, by definition, only of stretching.
- When Jake stretches, it is usually accompanied by a stretching, rubbery sound.
- Stretchy powers are the most seen and used ability in the series, appearing in almost every episode due to Jake being the deuteragonist.
- Jake's gender-swap (and species-swap), Cake, also has stretchy powers.
- While it has not been seen in the series, Jake is seen having the ability to fly by using his stretchy powers to turn his ears into bird-like wings in the Cartoonnetwork.com game, "Righteous Quest," as well as the sequel "Righteous Quest 2."
- In "Wizards Only, Fools" Princess Bubblegum's denial of magic includes dismissing Jake's "magical" stretchy powers as a mutation, foreshadowing Jake's true origin.
- His skeleton might have Stretchy Powers as well, as he describes them as his "squishy bones" in "James Baxter the Horse". Also, his entire body can shrink with him.
- Some of Jake's children are shown to fully/partly inherit Jake's stretchy powers.
- In "Jake the Dad," Jake Jr. can stretch her hair with shapes and size she wants, while Kim Kil Whan can stretch himself into two arms to form Super Pup with his siblings.
- In "Daddy-Daughter Card Wars," Charlie can instantly grow into gigantic size, reaching the outer space and walking through the Earth surface in seconds; as she grows bigger, she looks more transparent.
- Some of Jake's distant descendants in the future, known as the Pups, still have similar powers in sometime during their lifetime.