Superhuman Transfusion

"Anakin: What are you doing? Qui-Gon: You're going to need better stats. I'm transferring some of my mini-chlorines to your blood. Anakin: A blood transfusion? What?! Qui-Gon: They'll multiply there and grant you lightning fast reflexes and skill points in driving. Anakin: That's crazy!"

- Darths and Droids, episode 86

John has one or more Stock Super Powers of the genetic and/or magical variety. He may have gained them from birth thanks to Superpowerful Genetics, genetic experimentation, or after conception thanks to Super Serum, a Mass Super-Empowering Event or a Disposable Superhero Maker. Alternately, he has mystic powers in a setting where The Power of Blood and Blood Magic are very real, so his blood contains a measure of his magic. In short, his powers course through his blood in a very real sense.

Suddenly, his friend Jack gets shot by one of his enemies, and has only minutes to live before even his copious blood supply runs out! Just by luck, Jack and John are the same blood type, and a quick emergency transfusion ensues... which results in an Emergency Transformation. Thanks to the blood-borne nature of John's powers, Jack now has those same abilities! They might be temporary and last only as long as John's blood is in his system, or they may trigger a similar reaction in Jack's body and give him permanent (and potentially different) powers.

It bears mentioning that in Real Life blood transfusions in no way transfer the donor's genes into the recipient's DNA. The red and white blood cells last only a few months before dying without leaving a trace. If John's powers are biological/genetic/chemical in nature, and/or Phlebotinum is involved, Jack getting these powers is often justified by The Professor explaining that the donation triggered dormant super-genes in Jack, or actually did somehow overwrite parts of his genome. If John's powers are magical in nature, then the reason Jack gets similar powers may have to do with Blood Magic. In these cases "John" might not even be the same species as Jack, such as dragon or vampire blood endowing the imbiber with power. If John's powers are from a (symbiotic) virus, then it reasonably be able to transfer via blood transfusion, though you can probably count characters with these powers on one hand.

A subtrope of Super Empowering. See also How to Give A Character Super Powers.

Anime and Manga

 * In the manga Wolf Guy, Akira gives blood to Chiba after Hadou nearly kills him, and Chiba is healed by it and becomes a werewolf—and crazy, with the ability to change at will into some mutated-looking wolf-beast, unlike Akira's transformation. So, not a completely identical transference of abilities, but Akira didn't realize his powers would transfer at all.
 * In Futaba Kun Change Misaki gets the temporary ability to turn into a boy when she's transfused with Futaba's blood. Later justified as her latent Shimeru genes (apparently quite widespread in the Japanese population) being activated by Futaba's active genderbending factor.
 * In Rosario + Vampire, Tsukune receives a temporary Emergency Transformation from Moka by injecting her blood into him whenever he injures himself while protecting his friends. Eventually, it becomes permanent... with consequences.
 * Getting bitten by a zombie in Sanka Rea has this effect: the hydrangea that runs through their veins makes other people temporarily impervious to death or pain.

Comic Books

 * In Hellboy: The Island, Hellboy gets drained of his blood and a prophet of the Ogdru Jahad absorbs it. This causes the prophet to begin transforming into a copy of Anung un Rama, the demon that Hell wanted HB to be. The man is then driven insane.
 * Spitfire of The Invaders (Marvel Comics) gained superpowers from a blood transfusion from the first Human Torch. I'm not sure how that worked, given that the first Human Torch was an android.
 * This is She Hulk's origin. She needed a blood transfusion and Bruce was on hand, afterwards she was permanently changed into a hulk, albeit she retained her personality and intellect.
 * It later turned out that the Hulk's drastic change in personality is caused by a multiple personality disorder which is exacerbated by his transformation. She-Hulk's personality does change, but she doesn't have the insane number of alternate transformations that Bruce does.
 * In a Golden Age Superman story, Lois Lane dreams she gets a blood transfusion from Superman and gains superpowers, becoming Superwoman.
 * During the first arc of Young Avengers, Patriot claims that this is how he got his powers: his grandfather, Captain America (comics)'s supersoldier prototype, gave him a blood transfusion. It turns out be a lie (Patriot was addicted to a drug that gave super-powers), but then he takes a shot from a Kree blaster for Cap. When he gets to the hospital after the battle, Cap is all set for this, except "the other super-soldier beat you to it."
 * This is Deadpool's backstory; his healing factor was derived from Wolverine's blood.
 * The Savage Dragon once let his blood be used in an attempt to cure a friend's AIDS. It seemed to work at first—restoring him to full health, making him stronger, even giving him green skin and a fin—but within minutes, he exploded. Years later, after The Vicious Circle steals a supply of his blood from the hospital, their Evil Geniuses figure out a way to keep people alive much longer after being injected. But it turns out that regular doses are necessary in order to keep delaying the explosion, so when Dragon-blood-enhanced supercriminals get arrested, they end up exploding while in custody.

Fan Works

 * In Clan of the Mewtwo, a human who receives a transfusion of Mewtwo blood will be transformed into a Mewtwo.

Film

 * When Megamind finally succeeds at removing his Worthy Opponent Metro Man and is left with nothing to do, he ends up creating a new hero to fight by injecting some random joe off the street with Metro Man's DNA.

Live Action TV

 * The 4400 had an inversion. Isabel, the first child born to two returnees, produces pure Promycin. When all the other returnees are suffering from an anti-promycin drug, her blood cures Shawn who went on to use his own healing powers on everyone else.
 * In Dark Angel, when Max gives an emergency transfusion to Logan, her stem-cell-laden blood starts to repair his spine. Unfortunately, it doesn't last, but he eventually gets a hold of a mechanical exoskeleton that lets him walk again. Later, a transfusion from another transgenic has longer-lasting effects, which when added to the support from the exoskeleton let him be stronger and faster.
 * In Heroes Claire's blood can be used to heal other people through transfusion.
 * In the tv movie Deep Red. It has a girl whose blood rejuvenates the recipient and grants Voluntary Shapeshifting. In a twist, the power only lasts for a limited time, and regular transfusions are needed for people to sustain them. It's because of this that the bad guy, who has some of her blood in his system, is after her.
 * In Stargate Universe, Chloe Armstrong was able to cure lieutenant Scott with blood transfusion in episode "Cloverdale".
 * In Misfits, Nikki inadvertently gains the ability to teleport by a heart transplant from Ollie. She never learned to control it though.
 * In the final episode of Torchwood: Miracle Day:

Video Games

 * In Operation Darkness, a Werewolf giving his blood to someone changes them and gives them some kind of power. If they survive.
 * In Freedom Force, this is how Liberty Lad got his powers, Minuteman gave him a blood transfusion after his Reckless Sidekick behavior got him shot.
 * In Mega Man ZX, a "Mega Man" is a Maverick Raid survivor who harness the blood of the Big Bad Master Albert via donation. His blood (or rather, the contained DNA) is the key of unlocking the Biometal's power and allowing them to Megamerge with it.
 * This may not be a straight example: it's implied that Albert used his influence to get trace amounts of DNA into everyone through the upgrades that make Reploids and Humans essentially the same. The DNA lets them megamerge, but they still need the biometal to have superpowers. Not to mention the DNA may just be stored as data in both cases (since Reploids and Humans both have machine parts) and is simply submitted as a confirmation code when the person says "megamerge!"

Web Comics

 * There's a Penny Arcade comic where, after a car-crash, Gabe and Tycho end up in the hospital and get blood-transfusions. Gabe ends up getting blood donated by Spider-Man, and immediately develops web-shooting abilities, much to his joy. Tycho got monkey-blood.
 * Done deliberately in Darths and Droids; Jim had Qui-Gon give Anakin a blood transfusion so the mini-chlorines [sic] would make him Force-sensitive for the podrace. A later strip says that the Jedi tried it a few centuries ago, but the results were unpredictable.

Western Animation

 * There is an episode of Krypto the Superdog where the cat gets his powers this way.
 * Tex Avery plays it for laughs (natch) in the Walter Lantz cartoon "Crazy Mixed-up Pup". A man and his dog are run over and the paramedics give them transfusions, only the man gets canine plasma and the dog gets human plasma, resulting in a man acting like a dog and vice versa.
 * In Young Justice, this is apparently how they're handling origin, instead of the Super Serum from the comics. He had a life-saving blood transfusion from.