From a Single Cell

"I don't remember much after the explosion, but somewhere amongst the planetary debris the core of my being still existed, one living cell survived, and that is all I needed for my regeneration... Soon that living cell began to multiply into many, it wasn't long before I became conscious of my transformation, I could feel every part of my body growing, crackling with new life and energy. My shapeless mass began to sprout new limbs, first my legs, then my arms, and in no time, my whole body was restored!"

—Cell from Dragonball Z, having just survived his own Earth Shattering Kabooming Taking You with Me thanks to this trope.

The worst kind of unkillable enemy, there's the creature who cannot be mortally wounded, because he has a Healing Factor ramped Up to Eleven. Every injury simply regenerates, from lost limbs, to a blown off torso, to a broken neck. Even when you think you've completely killed him, he comes back, because you missed a bit of flesh that was able to replicate itself into a new body. He can even come back From a Single Cell.

This is rarely ever a trait of the hero; it is more often a power a villain has that marks him as being too powerful and resilient for the heroes to overcome, forcing them to find a creative way to beat the villain or gain a Plot Relevant Power Up.

If not properly explained, or given to a character who doesn't really seem worth it, it can become an Ass Pull. No matter how well done, it will have audiences (and characters themselves) screaming "Why Won't You Die?!"

Why every loose cell or drop of blood shed by the character doesn't generate a copy of them is not generally addressed. In a supernatural setting this can be handwaved with some talk about souls or lifeforce, though one still wonders how the various bits go about deciding which one of them gets to do the regeneration. Bonus points if the character/creature in question somehow retains all of his memory and personality (which are stored in the brain - no brain, nothing to restore all that data from!).

Expect this from all sorts of enemies, from demons, aliens, to androids made of Nanomachines.

A form of Nigh Invulnerability. A character who can regenerate this way and is The Ageless has Complete Immortality. See Shapeshifter Baggage and the necessary Genetic Memory. Also see Good Thing You Can Heal and Immortal Life Is Cheap. Related to Pulling Themselves Together.

Examples of From a Single Cell include:

Anime and Manga

Deoxys from Pokémon is shown to have this ability as long as its brain, the gem-like substance that protrudes from its chest (Which is pretty much indestructible anyway), is still active. While it can regenerate lost limbs in just a couple of seconds, it has been shown that regenerating its entire body can take up to several years.
Cell from Dragonball Z was a biological android with many of the main characters' abilities coded into his DNA, including Piccolo's regeneration and Freeza's ability to survive in very harsh conditions, meaning it overwrites Piccolo's one weakness of needing his brain undamaged. Therefore, he doesn't have to worry about dying if... say... the upper half of his body gets blown off. In fact, after initially losing to Son Gohan, he tries to blow himself up killing everyone. After the hero sacrifices himself to teleport Cell somewhere far away from Earth, Cell surprises everyone, including himself, by regenerating, quite literally, from a single cell.
- Cell has an unusual twist on this. Since he has Saiyan cells, he gets a zenkai whenever he suffers a near-death experience (like blowing himself up). So not only does he come back, he comes back several times more powerful.
- The next villain after that, Majin Buu, is a murderous, supernatural djinn, who can reform himself from a single piece of himself, and can reform himself if he is blown apart into a million pieces, or even air vapour. A single cell? All he needs is a single molecule. Planetary explosion? Give him 3 seconds. Blown up to shreds, the shreds then being vaporised just to make sure. Give him 3 god damn seconds. It took a Combined Energy Attack with power from every non-evil, non-dead character in the series up to that point to kill him.
Alucard from Hellsing, who can also use his spilled blood as a deadly weapon with no adverse effects. More than once was he reduced to a fine red mist before regenerating fully.
Rare heroic example: Yakumo from Sazan Eyes. He was turned into a Zombie Wu, an immortal undead slave, when Pai, the last of the Sanjiyan, sucked his soul into herself to save his life. His Healing Factor is so powerful he was once able to regenerate from being blasted into a bloody mist.
Elder Toguro from Yu Yu Hakusho does this, but he explicitly says that the only thing that will kill him is by destroying his heart or brain. Simple enough, right? Wrong. He's able to move around all his organs and body parts to wherever he wants in his body and can even ooze through cracks in the ground. Only two characters in the series manage do defeat him: Kuwabara (after transforming his Laser Blade into a Laser Racket in order to squash his entire body) and later Kurama (giving him a Fate Worse Than Death by planting on him a monstrous tree that never stops harassing its victim until his or her death, which will never be the case with Elder Toguro).
The Guyver can do this.
- Aptom from Guyver can also do this, although he requires Zoanoids to alter into more of his body mass (rather like The Thing, under Film). As a bonus, this also lets him use those Zoanoid's powers. The "why doesn't every part of him regenerate into him" issue is addressed - this will happen if they have access to sufficient biomass, but all copies of Aptom have a Hive Mind and can merge or split at will. Eventually, a villain finds a flaw in his power: after Aptom is nearly killed, his non-sentient remains are exposed to a Zoanoid which contains a fake "Aptom brain" and absorb it. His cells do not regenerate his brain due to thinking it's already present, thus allowing the villain to control Aptom's body through the fake. Sho questions why "Evil Aptom" keeps using an unwieldy Wave Motion Gun while fighting him, and realises that he has been using it to destroy any pieces of Aptom which were separated from the main body.
The berserked Self-Defense program in Magical Girl Lyrical Nanoha. Getting petrified and frozen didn't stop its regeneration. Getting blown to bits by three Wave Motion Guns didn't stop its regeneration. What finally killed it? A weapon that completely annihilates a target by distorting time and space over a wide radius, and it still would have come Back from the Dead had the first Reinforce not performed her Heroic Sacrifice.
Gemma the Depraved Bisexual from Ninja Scroll has regenerative abilities that may approach this level, but it's hard to say. In the movie, he reattaches his severed arm, reattached his head several years ago, reshapes his face after literally having it pounded into mush, and is finally drenched in molten gold and plunged into the sea, sinking to the ocean floor in a hardened coccoon of metal.
Tomie, the title character of a J-Horror manga series by Junji Ito and its subsequent film adaptations, can do this and can also speed the process up by infecting the bodies of other women and turning them into copies of herself. A scene in an early storyline implies that she is able to do this by virtue of being extremely radiotrophic, somehow converting background radiation into mass, as her growth was accelerated by a doctor's attempt to kill her with a radiation machine used to destroy tumors. Throughout the story its been proven that fire will kill Tomie for real and unable to regenerate (burned flesh are dead tissue)
Genji Ikusabe from Busou Renkin's spear has the ability to regenerate his entire body very rapidly, even if the body itself is completely destroyed. Admittedly, it has the weakness that he has to be holding his weapon at the time.
Rin from Mnemosyne (due to encountering a spore of the Yggdrasill tree) has virtual immortality, including the ability to recover from any injury, even getting sucked through a jet engine. Of course, being able to regenerate and stay alive under all sorts of conditions can be... bothersome.
Naraku from Inuyasha becomes like this (he starts off able to regenerate, but with limits). At one point he's reduced to his head, one hand, and miscellaneous bits of flesh and has regenerated fully within a chapter.
The Homunculi from Fullmetal Alchemist seem to be able to do this when their Philosopher's Stone is intact. Case in point: after one of his subordinates is grievously injured during a fight with the homunculus Lust, Roy Mustang attempts to hit two birds with one stone by forcibly removing Lust's Philosopher's Stone to kill her and using it to heal his friend. When the Stone is removed, Lust's body disintegrates, and Roy thinks he has won. Cue utter horror when Lust's body begins to reform around the Stone in his hand.
- Subverted in the manga, as there is a limit to how much they can regenerate, as their stone's power is limited, so you can kill them permanently if you do enough damage. Which is a lot.
- In the case of the Homunculi, the issue of why lost body parts and/or blood don't regenerate into copies is handled by the fact that a homumculus's Philosopher's Stone is the source of all its power. Thus, any part not connected to the Stone ceases to exist.
Mai from the H-manga Mai-chan's Daily Life can regenerate any part of her body as long as one part remains. In the end, they explain that the only way to truly kill her would be to grind her up or burn her to ashes. This makes her perfect for being a sex slave for BDSM inclined johns.
Nurarihyon from Gantz. Lets face it, without the gravity gun against this guy, you are screwed.
- Actually you might be screwed even with a gravity gun if something isn't distracting him.
Karkinos Rucan of Heroic Age was once completely destroyed, leaving only the core of his Heroic Tribesman. He gets better.
Touhou: Kaguya Houraisan and Fujiwara no Mokou are immortals who drank the Hourai Elixir (the legendary Elixir of Immortality), which makes the drinker absolutely immortal by effectively removing their death. Kaguya and her "rival" Mokou (and possibly Eirin herself) are the only characters known to have drunk it, and as a result have lived for almost two millennia (and counting) and are impossible to kill. While it's possible to inflict "mortal" wounds on them, they don't actually die and will quickly regenerate to full health. When fighting Mokou, a character with the explicit ability to kill anything wasn't able to kill her, and in the end she only stops fighting because of the pain (she can get hurt but not a single part of her is capable of dying).
- Of course, Kaguya and Mokou absolutely despise one another, and have killed each other repeatedly and futilely for centuries.
- Fairies respawn too, but are also said to have "a very short lifespan". What this means is unclear.

Comic Books

The Darkness had this once after Jackie set a warehouse and a few mooks on fire. The darkness survived by hiding in a tooth cavity, it didn't know what to do so Jackie got rebuilt.
Lobo of DC Comics, an alien mercenary who deviates back and forth from a Psycho for Hire to a Heroic Comedic Sociopath, can revive himself from a single drop of blood. He once cloned himself an army this way, but, y'know, being all "sociopathic," they all killed each other until one remained (in non-bloody ways, like suffocating each other).
One of the potentially toughest JLA foes was always the Shaggy Man, a nearly-invulnerable, ten-foot-tall bionic android that could regrow any limbs it lost almost instantly. Luckily, it was utterly mindless and therefore easy to trick. Eventually, a crazed general dying of brain cancer transferred his mind into it. He hasn't shown up very often since, probably because they're running out of ways to get rid of an unkillable, unsubduable villain with the mind of a brilliant tactician.
- Part of this may be because General Eiling found out too late that The Mind Is a Plaything of the Body. The Shaggy Man's tiny brain did not have a good effect on his mental facilities, and the Shaggy Man mostly just slept a lot. And yes, this does show a bizarre combination of the mind as the brain and as something beyond physical.
Characters who can change their shape or are made of something inanimate, such as Sandman, Hydro Man, and Clayface, are often implied to be able to do this.
- Superman villain Brainiac is constantly shown to be able to survive from the smallest remaining bit of his circuitry or computer program. This is taken to an extreme in the DCAU, where the tiniest bit of Brainiac always survives, is stored somewhere, and manages to take over more technology and reform himself completely. He is then defeated, and the processes repeats itself.
Master Mold from the X-Men acted much like Brainiac, storing backups of itself in out- of the way places.
- And its future "descendant", Nimrod, can rebuild itself if even a single molecule survives.
Isstvan, from the comic adaptation of Myth Adventures by Robert Asprin and Phil Foglio, gets blown up by a spell, and then rather squelchily reassembles. Nothing remotely like this happens in the original novel.
Wolverine once regenerated from a single drop of his blood landing on an incredibly powerful MacGuffin that was making the villain of the month all powerful. As a result, his healing abilities were supercharged to the point that he could regenerate from a single cell. He was also still touching the item when he popped his claws, (to destroy it) making it reasonable to assume he either deliberately or subconsciously used its power to re-adamantiumize his skeleton.
- During the Civil War Saga, he was immolated down to his skeleton and regenerated. Later comics apparently had him trade in some of his healing factor to return from the dead.
- A common Fanon theory about how he can make so many cameos in other comics is that every time he loses a piece of himself, it eventually grows into another Wolverine.
Deadpool also has regenerative properties. Unfortunately for him, it causes his cancer cells to regenerate rapidly too, causing him to be horribly disfigured and, well, not exactly sane.
Slippery B'eeef, the villain of The Authority: Kev had this ability.
Dr. Manhattan in Watchmen puts all these guys to shame. As Jon Osterman, he got disintegrated by radiation, to the point that they had nothing to bury. Somehow his consciousness survived and, in a few months, mastered command of matter to the point that he could remake himself from essentially nothing. Later, he is completely disintegrated again, and is back (and huge) in 5 minutes.

Doctor Manhattan: I'm disappointed in you, Adrian. I'm very disappointed. Reassembling myself was the first trick I learned. It didn't kill Osterman. Did you really think it would kill me?.

Daredevil of Earth X can do this—including ending up as many copies of himself after being torn apart by a mob. He even makes it into a circus act in which people try every method imaginable to kill him. Too bad for him he's a Death Seeker.
Swamp Thing once lost an arm, which grew back (for the first time in his book). Later, he met a mindless clone of himself which had grown from the lost arm. During the later Alan Moore run of Swamp Thing, he could dissolve his body at will and re-appear from any form of plant life whatsoever, anywhere in the world. (He later got exiled into space with help from Lex Luthor, though, but he managed to find a way to return.)
Modular Man from Tom Strong isn't quite at this level- he is, technically, mortal, and can be killed- but functionally he's identical: if even one of his modules exists, he can use it to make more. And he posted the plans for free download all over the internet...
Doomsday, The One Who Killed Superman, regenerated from being reduced to a skeleton. Lex Luthor helped by pouring some of Superman's blood on the bones to give him some raw material to work with.
Black Lanterns are zombies with power rings that can regenerate them back to full health, even if their entire body is destroyed. The rings themselves are Made of Indestructium.
Let's not forget Mister Sinister. As an aside, quite apart from this healing factor he has back-up plans in the event that someone does manage to kill him, namely that he secretly experimented on several characters in their childhoods (including Juggernaut, Professor X and Sebastian Shaw) to allow his mind to be transferred to them telepathically while their DNA is overwritten with his. So even if you stop him returning from a single cell, he'll still come back. Not helped by the fact that all three of those characters are quite hard to kill anyway, and one is nigh-invincible.
In the Silver Age, The Flash (Barry Allen) was a rare heroic example, as he was able to reconstitute himself from extreme fates such as being vaporized, apparently due to his complete control over his molecules. The one thing he couldn't save himself from, however, was being converted into energy in an epic Heroic Sacrifice.
The Incredible Hulk's "Maestro" incarnation was capable of regenerating from dust.
Juggernaut, while never having to regenerate from a single cell, is capable of regenerating from being completely skeletonized...assuming you can even damage him in the first place.

Film

One of the more dangerous qualities of The Thing (the shape-shifting Body Horror one, not the space carrot), provided it has biomass to feed on.
- The kicker? It only needs a single cell to consume you from the inside out.
Species: At one point a single cell is injected with the alien genetic material. It immediately starts dividing and growing, but is killed before it finishes turning into one of the Sil-type monsters. At the end of the movie it's implied that any part of one of the monsters can regenerate into a whole.
Frankenstein's Monster from Frankenstein Conquers the World. In fact, this results in the creation of the two monsters in the sequel, War of the Gargantuas.
This is how the title monster in the B-movie Reptilicus is created. A dinosaur tail, found frozen, regenerates into a full dinosaur once it thawed. It then goes on the rampage in Denmark. In the end, it gets put to sleep where they can then Kill It with Fire. Almost. A foot survived destruction, implying that it will regenerate and return again.
In The Fifth Element, the Action Girl protagonist Leeloo is regenerated from scratch in a rather cool sequence near the beginning of the film.
- Not to mention the nice Fan Service.
- The doctor who restores her practically quotes this trope when explaining the process, saying "A couple of cells are still alive. It's more than I need."
In the "Sorcerer's Apprentice" segment of Fantasia, Mickey Mouse can't stop the enchanted broom from flooding the room with water, so he chops it to bits. Unfortunately, each of those bits turns into a broom - complete with buckets already filled with water! - ready to continue the job.
At the end of The Spirit, it is implied that the Octopus, who has just been blown up all over an alleyway, will be able to regrow himself from a single finger.
Serleena from Men in Black II seems to have this ability.
T-1000 from Terminator 2: Judgment Day—its liquid metal parts can fully reassemble after having been frozen. Melting is another story, though.

Literature

The immortals of the Kage Baker "Company" series of books, well...it takes a LOT of destruction to get any of them to the point where they can't be brought back.
The traditional way to kill vampires in western literature involves staking, beheading, the burying at a crossroad at midnight with garlic in their mouths. They can still come back. Usually, the only way to truly kill them is to burn the body and scatter the ashes to prevent them from reforming, usually into moving water.
- Discworld jokes about the various and complicated methods of killing vampires by having vampires from different areas have different weaknesses. Furthermore, all vampires on the Disc can be brought back to life with a drop of blood - even if they were burnt to ashes. In fact, one vampire is a photographer for Ankh-Morporkh's newspaper and gets turned to ash every time he uses the flash. He carries around blood in a breakable vial so he instantly gets revived when this happens.
Margaret Weis and Tracy Hickman had monsters that could do this in The Death Gate Cycle. You had to stab a "chaodyn" in the heart, because if not they would heal and the blood that had dripped out of the wound would spawn a second chaodyn. (Killing them without spilling blood worked too.)
Blessed with Suck example from Orson Scott Card: Planet of Treason. One of the families exiled to an isolated world has genetically-engineered themselves to a state in which they can regenerate organs, so that they can sell them to eventually buy their way home. Occasionally a mutant like the protagonist appears whose regenerative abilities approach this level—but he also grows extraneous body parts that eventually cripple, then kill him. At one point, his guts are ripped out, producing a feral copy.
The book Jason X: The Experiment has Jason Voorhees coming back after being reduced to little more than a hunk of flesh due to being incinerated during atmospheric reentry. It takes him a couple years (even with help from Nanomachines) though.
The Animorphs frequently make use of the morphing power's healing properties. Their fights often go like this: Attack; get torn to shreds while decimating the enemy's defenses; de- and remorph; carry out the mission. Rachel in particular seems to lose and regrow limbs on a regular basis.
- Their regeneration ability becomes a major plot point in one book where Rachel morphs into a starfish and gets cut in half. She returns to her human form, but so does her other half, creating split personality Rachels, a decent, kind-hearted girl, and a total ruthless bitch.
Greg Bear's Blood Music takes a different spin on this. The noocytes are able to encode the squishy chemical versions of people into molecular memories based on DNA/RNA. The noocytes can rebuild and upload the original person - or an amalgam of anyone who wants to participate - back into a squishy flesh body should they so wish. After encoding and absorbing almost all biomass on North America, there are uncountable replicas of everyone to the point that there is no possible way to erase every copy.
One of the Star Trek: The Next Generation novels mentioned a race that fought a brief war with the Federation over this trope. Because they were effectively immortal, one of their more revered ways of learning things was by dying, because you usually at least learn "That was a bad idea." Because they thought every race had the same trait, they didn't realize that they weren't doing the Federation any favors by killing them.
In On Stranger Tides by Tim Powers, Blackbeard could regenerate from drops of blood falling from his severed head.

Live-Action TV

The Night Stalker (1974) episode "Primal Scream". An ancient cell sample discovered in the Arctic regenerates into a murderous ape man.
Grim reapers in Dead Like Me are effectively impossible to kill, being already dead. In the movie the cast try to kill a renegade reaper by shooting, drowning, and finally dismemberment followed by cremation and launching the ashes into space.
Jack King in Reaper could form a new self from just a hand. Possibly less, we never saw him try.
Ultraman Mebius had the villain Imperizer who had to at first have his entire body vaporized to kill it, otherwise, it would regenerate. Later it was toned down to destroying a certain part of it to prevent regeneration, but it was still Nigh Invulnerable beforehand. Worst part, they were the Big Bad's Mass Produced Minions.
The Replicators in Stargate SG-1 came close. It only took one active Replicator to make an entire swarm. Fortunately, they were limited by local resources, and there needed to be at least enough active blocks to form a working entity. They couldn't actually regenerate from a single cell.
The Doctor Who villain Eldrad first appeared as a fossilized hand, then having absorbed some nuclear radiation, turned into a walking hand. Eventually it regenerated into an entire person.
Captain Jack in Torchwood is not invincible, but always comes back to life after being killed, no matter how severe the damage. Even when in Children of Earth he is torn to shreds by a bomb planted inside his chest, and the only thing remaining of him is an arm, a shoulder, and part of his head, he regenerates fully within a few hours. He is conscious for most of it and it is very painful.

Oral Tradition, Folklore, Myths and Legends

There's at least one folktale where, when an evil wizard was burnt at the stake, countless birds and bugs burst forth from the fire, and all of them had to be caught and killed, for if just a single one escaped it would reform into the slain wizard.
A similar version appears in one of the more thorough methods of disposing of vampires. When you burn the body after staking it, chopping off its head and stuffing its mouth full of holy wafers, you have to drive back any rats or beetles that scurry out of the fire. It's not entirely clear what would happen if it did get away though.
In Hindu Mythology, the demon Raktabij could birth a new form from every drop of blood. Kali solved this by having the demons strangled. Part of the origin myth of the Thuggee cult.
- An alternative version is she cut off his head, then drank all the blood that flowed out.
The Hydra in Greek Mythology. Cut off one head and two grow back unless cauterized with fire.
- BAM.

Tabletop Games

Any Dungeons & Dragons creature with regeneration works this way unless you take its Hit Points to -10 with whatever form of damage it can't regenerate. A joke D&D item exists called "Troll in a Can" that uses this trope to turn a chunk of trollflesh into self-regenerating field rations. Wizards of the Coast ruled that eating a troll will eventually cause a new troll to grow inside you and EXPLODE OUT OF YOUR BODY. (Unless it's well done on a bonfire, since trolls do not regenerate fire damage and can be safely killed by it.)
- The tarrasque has this ability. The only way to defeat it is to beat it into unconsciousness and then use the most powerful spell in the game to make sure it doesn't wake up. (Good thing it sleeps 99% of the time.)
  - And as of Fourth Edition, the Monster Manual implies that the only real way to kill a tarrasque for good is to send it into space. Reducing its HP to 0 just sends it back to slumber beneath the earth.
  - Second Edition required the tarrasque to be reduced to -50 hit points, requiring the use of +1 or better magical weapons, then a Wish spell or equivalent to be used wherein you wished for the tarrasque to never return. Depending on your DM at the time, sending it into space may be a lot easier.
Mortasheen zombies work this way, given their absurdly powerful healing factor and the fact that their consciousness is spread out all over their body.
A similar abilty is possessed by the Hosts of the Werewolf: The Forsaken. These are bizarre hybrid spirit creatures (most commonly the Azlu and the Beshilu) who are able to either take on vaguely human forms or hide inside human skins. If a Host is destroyed, its body will shatter into dozens or hundreds of its animal form (which will look like mundane animals), one of which contains its soul. They all need to be destroyed to be safe or else they will eventually consume enough to regrow into their monstrous forms (and usually be pissed at whatever killed them).
- In World of Darkness: Immortals, we have the Purified, who have this as one of their main abilities. You see, they've turned their souls into spirits, and like the Hosts above, just killing one's body simply sends his mind to the Shadow, where they can rebuild it even if it was completely destroyed. They're a perfectly viable character option (far more so than the blood bathers and the body thieves), and this ability is mitigated by the fact that the Spirit World is rather dangerous. That still means a halfway competent Purified is going to alive for a very long time (this is a book called Immortals after all), but it's something of a weakness.
The Ananasi and Kumo (werespiders) in Werewolf: The Apocalypse could break into swarms of normal-sized spiders (called the Crawlerling form). If a single spider from the swarm survived, it could eventually hunt enough to increase its mass to the point that it could resume human form. (Unfortunately, the Ananasi in such a situation would probably lose almost his entire memory...)
In GURPS, this is the 100-point level of Unkillable. For just 50 points more, you don't even need that one cell.
While the Necrons of Warhammer 40,000 don't have cells, being automatons, they fit the spirit of this trope, able to regenerate or be repaired from any damage whatsoever. Well, at least originally; newer versions seem to have Nerfed that ability into oblivion.
- Tyranids are this trope on an interstellar scale, when considering that their Hive Fleets and Hive Mind are really just one big body. If even one vessel manages to survive and reaches an ill-defended planet or three, they can use the biomass to rebuild the entire fleet.
- Da Orcs on a species scale, since they reproduce by fungal spores, all they need is a single spore left over from battle and untouched by cleansing flame to sow the seeds of a new invasion.
- The Expanded Universe brings us the Halo artifacts, which... well, see Nightmare Fuel for details.
Magic: The Gathering has Squee, the goblin who, as both Crovax and Ertai learned, could never stay dead. Ever.
- On a larger scale, we have the Phyrexians. As long as a single drop of glistening oil remains, they can be reborn continuously, forever.
This (along with being The Ageless) is basically how the immortality of the gods of Exalted works. You can destroy the body of a god, but as long as they have a sanctum, they'll just regenerate there (note that all Celestial Gods count the Heavenly City as a sanctum). The only exception to this is if they're finished off with a spirit destroying Charm, which essentially ignores their immortality. All Exalted possess spirit killing Charms.
- Also, Chimeras - Lunar Exalted who have gone bat-shit insane - can learn this. The Knack is called "Perfect Regeneration", and also solves the question about "which part regenerates"; the Chimera's spirit will always occupy the largest remaining part. This lends itself to some interesting ideas about how you could permanently kill it with relatively mundane methods, but since we're talking about an Essence 6 Axe Crazy shape-shifter-slash-titan-killing-weapon-gone-rogue, it might just be easier to pop a Total Annihilation on it...

Video Games

Xenosaga's Albedo Piazolla may be the single most indestructible example on this page. It takes a Cosmic Horror to kill him permanently, and even then, he comes back. The third game ends with him asleep in his twin brother's subconscious mind, with the implication that this might not be a permanent arrangement...
Touhou's Fujiwara no Mokou and Kaguya Houraisan. The Hourai Elixir they drank granted them immortality and the ability to come back to life even if their bodies were completely destroyed.
- It goes beyond that. Yuyuko has the ability to kill anything by simply inviting it to its death, and once attempted to use it on Mokou. She couldn't even find her death.
- Marisa, being Marisa, lampshades it by asking what every one of us has always wondered: if we split her in half which half will regenerate?
Jenova from Final Fantasy VII can apparently regenerate indefinitely so long as some cells still exist.
- Which is what provided the retroactive Sequel Hook: Cloud (and others) are infected with Jenova cells, and thus Jenova and Sephiroth are not truly dead, but, in fact, possibly more powerful than ever.
Also from Final Fantasy, Exdeath of Final Fantasy V once rebuilt himself from a single splinter.
Roa from Tsukihime can be like this, but only when the conditions are absolutely right (midnight during a full moon, as Arcueid found to her chagrin, when he regenerated from his ankles up).
At the end of Prototype, Alex Mercer saved New York from being nuked by flying the nuke out over the ocean. Unfortunately, he didn't escape the blast, and a few mangled fragments of him wind up in Manhattan. A crow eats the pieces; which then eat the crow. Alex rebuilds himself from the inside out.
Every single enemy in Metroid Fusion works this way. Since they're all X-Parasites mimicking various creatures, they revert to the cellular form when defeated. The only way to kill that form is to absorb it (which only Samus, or a metroid, can do). If the cell form isn't absorbed, it recreates its body or infects the killer. Some can even spawn more cell forms, creating even more monsters. Needless to say, had anyone other than Samus been there, the universe would have been screwed.
- Ridley also seems to have this, as his entire body routinely explodes.
- The Metroid Prime AKA Dark Samus also has this quality, suviving everything up to and including being vaporized and then caught in the destruction of an alternate dimension immediatelly afterward. The 100% completion ending of the first two games of the Prime trilogy basically just show the player that, yep, it's still alive and kicking.
The Flood of Halo are this trope on a much larger scale. From a single spore the Flood can rise again.
In The Powder Toy, most forms of 'exploding' life will regenerate no matter what you do.

Web Comics

Xykon from The Order of the Stick is able to regenerate from any injury as long as his Soul Jar still exists. After his first (and so far only) defeat, he was notably ably to regenerate his whole body from essentially nothing.
- This is a standard ability of all Liches in DnD.
Schlock from Schlock Mercenary kind of does it here. When 80% of his body mass is incinerated in an explosion, the remaining mass is able to re-assemble into a sapient individual- but Schlock loses most of his mind in the process, (it's spread throughout his body) and regresses to a child-like state. It's implied that while his memories are gone for good, in time he'll eventually just grow up into an adult again.
- Or he would if he hadn't Time Traveled back into the past and merged with his alternate-universe counterpart. Thereby also answering the question of what happens if he gets split in half.
In Problem Sleuth, Demonhead Mobster Kingpin's 2nd form had 3 health bars, all regenerating extremely quickly. However, if you knock out a health bar, it's gone for good. His 3rd form had enough bars to, from the center of the universe, physically break into hell and he could regenerate entire bars just about whenever he wanted to.

Western Animation

Amazo in Justice League and Justice League Unlimited is made of Nanomachines, and thus he can reform from any injury that doesn't completely destroy him. However, this was subverted at first because he only gained the ability to do this after he copied the Martian Manhunter. Before that, a small explosive in his brain really would have killed him.
- This trope was double-subverted in a later episode. In an Enemy Mine assault against Amazo, Lex Luthor and the League use the robot's blueprints to build a weapon capable of disabling its nanomachines. However, it's soon revealed that Amazo knows about this limitation, and had evolved itself beyond the nanomachines' tech threshold, rendering the weapon useless.
The Itchy and Scratchy parody of The Sorcerer's Apprentice has thousands of Itchys regenerating after Scratchy chops him up into fine dust. Unfortunately for Scratchy, they regenerated after he inhaled some of that dust.
Bushroot in Darkwing Duck, as a plant/duck/thing, can regenerate even if there are only tiny vines left of him. Through the whole series, he's been mulched at least twice.
This once happened to General Skarr on The Grim Adventures of Billy & Mandy when he became a plant like being after coming in contact with Grim's scythe. At the end he is blown through the air by an exploding lawn mower and is chopped to pieces by a helicopter and we see him slowly regenerate later.
In the SpongeBob SquarePants episode "Franken Doodle", said doodle recreates its body by redrawing itself with a magic pencil.
Danny Phantom has two dangerous enemies with this kind of power: Undergrowth and Nocturne. Apart from instant recovery from Danny's attacks, this trait is made apparent when Undergrowth managed to (offscreen) completely regrow his body after it was blown to nothing but a weed and Nocturne was able to pull himself back together after Danny froze him solid and shattered him.
The Big Bad of Generator Rex Van Kleiss is able to rebuild his entire body using the nanite-infused soil of his homeland. He did this near the end of the first episode after Rex smashed him to pieces.
In the first animated Star Wars:Clone Wars series we've got alien bounty hunter Durge who has incredible healing powers. We see him recover from been cut into half, and later in that series he got blasted into a gooey mess via the Force by Obi-Wan. The schocker: Durge still survived this in other works! He was finally Killed Off for Real by Anakin, who hurled him into a sun.
The R.E.G.I.S Mk V. If there is sunlight and a small piece of it remains, it will reconstitute itself.
In The Penguins of Madagascar, the penguins clone a whole dodo out of a single feather. When said dodo dies minutes later because he's stupidly reckless, they reclone him from one remaning feather, and he acts as if nothing has happened. This gets repeated all throughout the episode.

Real Life

Sea squirts can literally regenerate grow new bodies from a single blood cell.
Some species of flatworms and starfish have impressive regenerative abilities, and although they can't grow back from a single cell, a single individual can survive being cut in half and both halves can independently develop into complete, separate individuals.
A few examples from the plant kingdom—Cultivars are specific clones of certain plants (such as a Fuji Apple, or a Red Dragon Venus Flytrap). You can't grow these by just making seed and hoping the new plant is identical to the parent—you have to cut off a piece and force the plant to spit out new roots.
- Another plant example is Micropropagation—that is, taking a single cell of a host plant, putting it into some special goo (essentially extremely sugary jelly), and letting the cell clone itself a few thousand times, all through a process called Tissue Culture. It's difficult to do, being extremely expensive and time consuming... At least it was; nowadays you can do it in your kitchen. Isn't science grand?
- Not to mention the innumerable weeds/invasive plants that just excel at that asexual propagation stuff. Any plant cell from an asexually-reproducing plant has the potential to become a new plant. Many a gardener have probably screamed Why Won't You Die? whilst uprooting creeping charlie on their hands and knees.
- Caulerpa is an extreme example. It's normally a seaweed (technically a single-celled algae, making it a literal example of the trope) native to the Caribbean and a few other tropical seas. However a combination of a mutated variety capable of surviving in subtropical and temperate waters, a natural toxicity and the ability to grow back into a full plant from the smallest fragments has turned it into one of the most dangerously invasive aquatic species on the planet. Because of its incredible regenerative ability, the only effective way found so far to combat a Caulerpa outbreak is to sterilize the entire outbreak area of all life and let the native life recolonize the resulting aquatic desert.
Sacculini carcini is a hellish parasite that combines properties of the Alien and the Puppet Masters or the Goa'uld. Its larval form attaches to a crab and injects just a few cells, which grow into a sluglike thing that lives in the crab's abdomen and grows a set of tendrils throughout the crab's body, including into its eyes. It controls the crab's behavior also, making it eat constantly to feed the parasite and making the crab care for the parasite's eggs. In a female it seems to be activating maternal behaviors already there, but /male/ crabs take on the same behaviors when infected.
All totipotent cells, most commonly found at the start of an organism's development before mitosis gets too far under way. Prior to a certain point, splitting the developing zygote apart results in identical twins.
- Sponges contain totipotent cells throughout their bodies when mature, potentially giving them the full version of this trope.
Nematodes. Not only can they regenerate from a single cell, they can eat themselves till being reduced to one cell if they don't find food, and then regenerate from that single cell left.
Cancer. If there's even just a few cancerous cells left in an individual, they'll continue to rampantly grow and divide and continue the disease. This is why metastasized cancers are so dangerous, it's extremely difficult to ensure that all the abnormal cells have been destroyed or removed, and that there aren't any more floating around in circulation somewhere.
- Most notably the Hela cells, the first immortal human cell line. They were taken from Henrietta Lacks's cervical tumour in 1951 and they're still going. They will also invade and take over any other cells you happen to have growing about the lab - they've done millions of USD worth of damage that way, but it's sort of balanced out by also being responsible for every significant medical discovery in the past sixty years.
Life as we know it. It must have started somewhere, meaning it could happen again.