Huntress: I take it that something went terribly wrong at that project—? DarkClaw: Actually, the program was a resounding success. It produced exactly what it set out to produce: a remorseless killing machine devoid of all human compassion. A perfect weapon. They forgot one important thing about weapons. They are usually inert objects that can't get off the table and do harm by themselves. Their mistake was in creating a weapon with an imagination.
This is the use of a living creature as a weapon. This is usually simply a subtrope of Organic Technology; an otherwise normal, user controlled weapon which happens to be a living thing. To qualify, 1) it must be alive when it is used note So a slingshot made from a springy Y shaped branch doesn't count, but if it was still attached to a living tree it would and 2) it must be separate from the user note so claws don't count, since they're part of the creature that uses them; removing the claws from a creature and strapping them to your hand doesn't count since they're no longer a living thing, but a creature that happens to resemble a claw shaped glove that could be worn by another creature would.
This also has a few subtypes, examples of which go on their own pages;
The EVA units from Neon Genesis Evangelion. They are Eldritch Abominations with restraining bolts tightened on them to keep them in control. Once that armor goes off, watch out. To make them sync with the pilot, the people who make the EVAs have to bond a soul of their mother to the EVA, though the details aren't exactly clear, with one unit having the entirety of the soul, another just having part of a soul, and another just having a clone's soul. In any case, if the pilots come to harm, especially if it's Shinji, watch out.
An interesting example is Crona and Ragnarok from Soul Eater. The result of a witch's experiment, Crona had all of hir blood replaced with a substance called "Black Blood" (not 'that' Black Blood) that was created in part by melting down the Equippable Ally Ragnarok. The result is a mentally unstable Tyke Bombwhose weaponized blood has its own distinct personality.
Half the characters can willingly transform into weapons; some can actually move somewhat independently or just transform body parts into weapons if they don't have a meister to fight with. This came about as the result of another witch's experiment centuries earlier (the sister of the witch who created Crona and Ragnarok, at that), and now many of the descendents of her test subjects have inherited the ability to transform into weapons.
Baby 5 from One Piece ate the Weapon Weapon Fruit (Buki Buki no mi), allowing her to both form weapons from her body parts and/or turn herself into large weapons including torpedoes (she can reform after the explosion), scythes and swords.
In Katanagatari, practitioners of Kyotouryuu like Shichika have it indoctrinated into them from an early age that they are swords, not swordsmen. They aren't supposed to think for themselves and should only attack what their "wielders" want them to attack. A big part of Shichika's Character Development throughout the series has him realizing that he is more than a sword.
Majin Buu from Dragon BallZ was a nearly mindless Pure Magic Being created by the alien wizard Bibidi for the purpose of universal conquest. Since Buu was essentially destruction incarnate, even Bibidi couldn't control him. Bibidi treated Buu like a bomb: he'd drop Buu on a world, unseal him and let him wreck havoc for a while, then promptly seal him again. Buu mellowed out (relatively speaking) after absorbing a few Grand Kais and taking on some of their traits. He was still a dangerous monster, but he wasn't focused on destroying things all the time after that.
In Fairy Tail, Franmalth, one of the Nine Gates of Tartarus, boasts that the Nine Gates are biological weapons that Zeref created to be able to entire armies by themselves. They are wholly devoted to their creator Zeref and do their best to fulfill his wishes...despite never having even met him.
The Samehada (lit; Sharkskin). A living and sentient sword seemingly made from super hard sharkflesh that forms a symbiotic relationship with its wielder and has the ability to eat its opponents flesh and/or energy.
The Ten-tailed Beast. Unlike the Beasts that followed it, it lacked sentience. The God Tree was just that: a tree, with no mind of its own. Its rampage in the distant past was actually the work of Kaguya who was sealed within it, using its body and power in her attempt to regain her monopoly on chakra.
The Weapon X project, full stop.
Wolverine was enhanced by Weapon X precisely with this purpose in mind.
X-23 was grown in a lab by the Facility using genetic material salvaged from Logan in an attempt to restart Weapon X, and the project leaders made every attempt to strip her of her humanity and turn her into an emotionless killing machine and hired assassin available to the highest bidder. Even after escaping Laura continues to find herself being used to kill. That she doesn't want to only ever be a weapon and greatly desires a normal life is a major part of her character. The Trigger Scent is able to force her to become this against her will. If someone is marked with the scent, "Laura" vanishes and is replaced by the ruthless and horrifically efficient weapon the Facility wanted her to be and only returns after her target is dead.
In Prometheus it is learned that the xenomorphs are genetically engineered superweapons. Disturbingly enough, humans were created from the same black liquid that created the Engineers' other monsters.
Harry Harrison's West of Eden books feature the Yilanč, a race of intelligent amphibious reptiles, who rely entirely on bio-technology, including Bio-weapons.
Shiftblades from The Deepgate Codex are souls of the dead conditioned to serve as weapons. Most remain in weapon shapes at all times, making them this trope, but one example in God of Clocksalso takes human form.
The two runeblades, Mournblade and Stormbringer, from The Elric Saga are soul-eating demons in the form of swords.
The Hork-Bajir in Animorphs probably fall into this...they are technically separate from the Yeerks controlling them, but are under their control as weapons.
The Speaking Gun from Simon R. Green's Nightside series. A conglomeration of flesh, bone, and gristle made to look like a weapon, it is a sentient creature that longs for the destruction of everything.
In the Sword of Truth, the Great War was full of these. Mriswith, Confessors, Dreamwalkers, the Travelling Well, and even to an extent the Pristinely Ungifted were all made into lethal weapons in the old war. Most of them were born as wizards or born to wizards, but treated more like tools than people.
The Seeker of Truth and his titular sword. Richard wasn't kidding when he bragged that he was the weapon. The sword is:
a magical morality pet
a repository of accumulated knowledge of fighting and war
a teacher of War Wizardry
a focus for the instinctive magic of War Wizards
The Wheel of Time has the man with two souls, a fearsome warrior with one soul fully committed to protecting himself in the real world and the other fully present in Tel'Aran'Rhiod.
Before the Myrddraal started appearing, the Trollocs were equally dangerous to both Light and Dark, and were deployed as expendable, living weapons.
Immortals in the Codex Alera are slaves raised using discipline collars to enjoy pain. Nearly unstoppable, if also nearly mindless, storm troops.
The Vord warrior forms, as is par for the course with zerg/tyranid-style hive minds.
It's an open question whether True Shardblades from The Stormlight Archive count as this, given that they are in fact a shapeshifted version of the Energy Beings known as spren, which can think and talk but have no physical body and so aren't "alive" in the scientific sense of the word. The more common regular Shardblades probably don't count, since they are spren whose minds were destroyed by the Recreance, and are much more like corpses than living creatures.
Live Action Television
In Doctor Who, the Moment is a weapon created by the Time Lords that developed sentience and a conscience. It was shelved despite its immense power due to its potential unreliability. It is fully capable of preventing itself from being used if it disagrees with its user. The Doctor intended to use it to end the Time War by eliminating both sides — but instead it helped him find another way. All thirteen of his incarnations together shifted Gallifrey into stasis in a parallel universe, while appearing to destroy it.
Time Lord General: How could you use such a weapon, knowing that it would sit in judgement of you?
Before the Moment, there was the living metal validium, created as Gallifrey's ultimate defence. Unlike the Moment, it lacks the ability to go against its user's wishes.
"Ophitech" in the Tabletop Games setting "The Day After Ragnarok" falls under Type 3.
Magic: The Gathering has had occasional mentions such as the Dancing Scimitar and its spiritual sequel, Ensouled Scimitar. But there's also a whole group of artifacts called Living Weapons, which are equipments that come with their own hideous Phyrexian token creatures already attached. Considering that Phyrexian culture consists largely of mutilating and cyberneticizing each other into giant living weapons, and then beating the crap out of each other, this is pretty typical.
In Warhammer 40,000, Tyranid weapons are specially-evolved organisms fused with their wielders in a symbiotic relationship, frequently firing living ammunition. This even extends to some Tyranids, as the Hive Mind is willing to expend them like ammunition, so that some organisms are bred to fight a single battle.
In the distant past, the Old Ones uplifted or bred servitor races to help them fight against the Necrons. They certainly succeeded with the Orks, a species that has since outlasted its creators, lives only to wage war, and will happily fight each other if no other foe is available.
The Exalted are this, in a sense; they were made as independent weapons, simply because any form of control would utterly defeat the purpose of creating them in the first place. Less metaphorically, there exist ways to awaken the Least Gods of things, helltech involves the use of still-living demons to empower artifacts, and Craft: Genesis has done some interesting things with artificial lifeforms. Soulsteel weapons technically don't qualify, as while they do contain sapient (and eternally suffering) souls, they are usually dead.
World of Warcraft features a number of weapons that are alive. Such as the Dark Edge of Insanity, an axe that drops from an Old God. The axe itself appears to be covered with black reptilian skin, and is adorned by a huge yellow eye, that BLINKS and turns in its socket. Another example is Terestrian's Stranglestaff, the upper end of which consists of a rather disgusting octopus-like creature with squirming tentacles and a beak. And Zhar'doom, Greatstaff of the Devourer, is actually a Zergling/Felhunter-like creature stretched to the form of a staff. The head of the beast is the head of the staff, which clacks its jaws littered with very sharp teeth, and lashes forward with its tentacles.
The Mogu created the lizard-like Saurok as a living weapon to police and control their empire. The Saurok were too wild to be controlled in such a manner and eventually rebelled against the Mogu.
Lorewalker Cho: There is a problem with creating a living weapon... Who now wields the power?
Half-Life has the Hivehand, basically a living alien beehive which shoots a constantly replenishing supply of bee-like aliens. There's also the Snarks. If you can get some from their nest, you can sic them on enemies, where they'll pester them rather effectively until they either get smashed or blow themselves up.
The Tactics Ogre games have a spell/scroll called Snapdragon that allows you to turn an ally into one of these.
One of the calling cards of Oddworld: Stranger's Wrath was its spin on the idea of "live ammunition". To explain, Stranger uses tiny living creatures as ammo for his crossbow (each with various effects).
Daedric weapons and armor in The Elder Scrolls games are created by binding the spirits of lesser Daedra to the forging materials. In Skyrim this is done by using Daedra hearts while smithing. Since Daedra are immortal (their physical bodies can be destroyed, but their spirits endure), this means that every Daedric weapon and armor piece is still alive. Fortunately, since each Daedra is an immortal Time Abyss, being used as a weapon or piece of armor for a century or so (Daedric artifacts vanish on their own after a while) isn't really a big deal.
Kingdom Hearts has the Big Bad from the first game, Ansem, who fought with a monstrous Living Shadow known only as the Guardian; it seems to have no will of its own and merely acts as a weapon for the character.
Drudge weapons from The Conduit are basically this. They groan when you pick them up, use biomass as ammunition, and even breathe.
In Halo, Hunter teams (each a bonded pair of Hunter colonies in armor) are deployed more like equipment than infantry.
Halo 3 revealed that Scarabs are just really big Hunters.
Shadows Of The Damned has Garcia's sidekick Johnson, a demonic skull-torch who can transform into various guns. His default form functions as both a torch and Garcia's melee weapon.
There's a reason that the mutant monsters in Resident Evil are called B.O.Ws, or "Bio-Organic Weapons". The whole point behind Umbrella, and later organisations, is to engineer living weapons.
The Honedge line from Pokémon are this; amusingly, they look pretty similar to the pictured Soul Sword.
In Sword of the Stars, the Liir "biological weapon" known as "the Black" that all but wiped out the Suul'ka is a gigantic Liir Elder with an environmental support suit similar to the Suul'ka who has dedicated his life to eradicating them.