A common type of enemy, an Asteroids Monster is a creature of significant size that, when killed, splits into several miniature versions of itself. Sometimes, killing these may result in further miniature versions, which may in turn split into even smaller versions. There can be any number of stages, although three seems to be the most common number. The Asteroids Monster is often also a Blob Monster.
The miniature versions may grow to normal size if they are not killed quickly. Also, the smaller asteroids tend to be faster than the bigger versions, thus making them even more dangerous. The Asteroids Monster is typically not a boss, but are usually Demonic Spiders or at least Goddamn Bats. It occasionally shows up as the Mini-Boss.
The Asteroids Monster is named after the arcade game Asteroids, which featured asteroids that would explode into two small asteroids when hit, which could further be split into even smaller asteroids. The smaller the asteroid, the more points it was worth.
Related to Hydra Problem. Contrast Weaponized Offspring.
Tsunade's summon Katsuyu, a giant slug, can similarly split, although it can't grow in size/number and doesn't need to be attacked to split.
Impel Down in One Piece has the aptly named Puzzle Scorpions. They look like a giant centipede normally, but divide into about a half-dozen poisonous scorpions if struck.
Punk Hazard is home to Smiley, a blob with similar splitting powers. No one, not even the Straw Hats, are able to defeat it. It only goes down when it eats some candy its creator Caesar Clown prepared for it, which causes it to self-destruct into a WMD.
Tomie takes this to the logical extreme. The titular character is an Eldritch Abomination who has an incredible healing factor. Stab her? She heals. Chop her to pieces? Each piece generates a new Tomie. Slash her up without actual dismemberment? nasty things happen.
ZOUSHOKU SHOUJO PLANA-CHAN!, had the heroine Rinne Ikaruga forced take care of her Mad Scientist sister's genetically engineered mutant half planarian (a non-parasitic flatworm) 4-year old named Plana. Due to the regenerative abilities coming from her planarian half, Plana is able to instantly split into more of herself much to Rinne chagrin, as simply tripping causes Plana to instantly multiply into more Planas (including smaller ones). Fortunately for her (and the entire town should it get overcrowded with numerous little mutant girls), limitations to Plana's splitting ability make it so that separating into 30 parts causing all Planas except the original to instantly disappear.
In Puchim@s, Haruka-san multiplies if she's doused with water.
The Zylons from DC Comics' Star Raiders graphic novel. A Zylon that's been blasted into a dozen pieces will soon regenerate into a dozen Zylons; the only way to completely destroy one is to send it into the vacuum of space.
In a variant, when Ash in Army of Darkness is grabbed by his own reflection, he breaks free and the mirror it'd leaned out from gets broken. As soon as he turns his back on the broken pieces, a bunch of miniature Ashes emerge from the fragments and gang up on him.
In The Thing (1982), every cell of the Thing is an independent organism. At various times during the film, it gets parts chopped off it, which grow new appendages and scuttle off.
The Green Slime is like the Thing, except it absorbs energy directly to grow and isn't infectious. Every time its cut or injured, it can heal its wounds and the cells in its blood will form new members of its species.
Hellboy: The Sammael monsters are part this trope, part Explosive Breeder. When one is killed, its life force will leave its body and split in two—causing two of the eggs it had previously laid to hatch and grow to adulthood in seconds.
According to one Jewish interpretation of The Bible, the plague of frogs started with just a single frog, which split into two every time it was hit. The Egyptians nevertheless were so annoyed they couldn't stop hitting it, ending with the whole Egypt being inundated.
In Star Tiger by Christopher Anvil, the only creatures on a planet appear to be placid herbivores. But if you kill one and don't destroy the body completely, what's left regenerates into one or more smaller, vicious carnivores, ranging in size from a tiger down to a shrew.
The Dresden Files has the 'Mantis Girl' Denarian, who turns into a bunch of little mantises when blown to bits. They all come back together to re-form the larger self. It also has Lea's guardian worm, which turns into two guardian worms when blasted.
Trolls bleed miniature versions of themselves and can eventually reform from the smaller parts.
Sheri S. Tepper's squicky novel, Shadows End had genetically engineered little boy designed to be the virus a bunch of monsters called Kachi. One of the monsters chews up the boy and spit out the pieces which end up becoming 120 smaller versions of the boy, some as small as half a finger with the biggest being leg size.
Non-aggressive example: In Mid-Flinx, one of the bizarre things Flinx sees in the jungle is a worm-like many-legged shape which, when it falls off one branch, "shatters" into several short animals on the one below. These scurry around for a bit, then link up head-to-rear as a single crawler again, thus maintaining the illusion they're one larger and less-vulnerable animal.
Ochre Jelly. If you don't have blunt weapons, you'll end up with forty jellies with 1hp each.
"Pudding" monsters break into two fully-functional halves when hit with a bladed weapon.
Neogi Old Masters teem with young Neogi slowly eating them from inside. When it's dead, little nasties will evacuate, then try to eat everything meaty in sight.
Adventure I3 Pharaoh. The PCs can encounter Chabang Men. If hit with a cutting blow, they split apart, collapse into mud, then spring up as two new Chabang Men. They can be neutralized by pinning them to the wall with spears or other stabbing weapons.
Adventure IM1 The Best of Intentions. The Firemaster smashes a fire elemental with his fist, splitting it up into 24 smaller elementals that scurry off.
First edition trolls were like this, although it took some time. In other words, if you kill a troll by hacking it to pieces, be sure to burn the pieces. In later editions, only the biggest piece would regrow.
The 3.5-edition Monster Manual 3 has a variation with the omnimental, an elemental composed of all four classical elements which, when killed, splits into one creature for each element.
Once upon a time, Horrors of Tzeentch in Warhammer did this - "Pink Horrors" split into weaker "Blue Horrors" when wounded. The rules no longer reflect this aspect of the fluff, "for the sanity of the players."
ManyTower Defence games feature a "split" enemy, that, when defeated, splits into two smaller but weaker enemies.
The most extreme example of this trope in TD games is the good old Bloons Tower Defense games, where every bloon exept the red one has multiple bloons inside of it. This is especially the case with M.O.A.B.-class bloons...
Blaster Master Overdrive featured a squid-like enemy in later levels that pushed this trope Up to Eleven.
Titans in Guild Wars did this whenever encountered, often having a physical titan turn into a magical titan when killed which would then split into two physical titans, making for a very long fight. Note that only the ordinary titans did this, stronger titans and bosses did not, which paradoxically meant that you were often relieved to see a more powerful enemy when low on health.
Gradius 3's second stage was filled with large bubbles that split into four smaller bubbles when destroyed. More akin to stage hazards than enemies, but a decent example nonetheless. The Lethal Lava Land stage had lava bombs that split into smaller fragments, which were indestructible in the arcade version/
Heart of Darkness featured a rather nasty cyborg who when killed was reduced to two lumps on the ground... which respawned into cyborgs if you didn't kill them quick enough. When you first encounter him this is a nightmare as you have to use a slow charged attack in order to destroy them. It got easier once you had your gun back.
The Jub-Jub ghosts in the Neopets Magax game. And since all the enemies in a given stage have a tendency to grow, it's not uncommon to wind up with three normally-sized enemies to deal with.
Zols and Vires from The Legend of Zelda I split into two monsters, but only if struck with a weapon under a certain power level. In order to get items from them, Zols require the White Sword (or equivalent: Arrow or Magic Rod); Vires require Magic Sword or Bomb. There's also the noise-sensitive Digdogger, a boss example.
The Floormaster is another example, as the larger Floormaster does a given amount of damage from hitting you, but once it's split, the smaller mini-Floormasters can grab you and take out the same amount of damage every few seconds. And given enough time, they will grow into full-sized Floormasters.
In The Legend of Zelda: Twilight Princess some strange edible blobs called Chu (which can go both ways, smaller junks can congeal to form a larger enemy); since each small Chu comes in a different color, it's important to avoid the merge if the player seeks to scoop the remaining fluids they leave after being killed. Chuchus in The Legend of Zelda: Skyward Sword are an especially annoying variant; as in Twilight Princess, they split into smaller Chuchus when sliced, which can re-combine into the original Chuchu, at full health. Additionally, if you slice horizontally, they split vertically, instantly falling back together. Only the smallest sub-Chuchus can be killed with your sword, and the biggest ones contain eight small ones, some of which might appear momentarily after 2 hits with your sword. Chuchus of any size can grab you and prevent you from attacking. And some of them can electrocute you through your sword when you hit them.
Jalhalla, boss of the Earth Temple in The Legend of Zelda: The Wind Waker, splits into multiple poes when injured. Link must then kill as many of these poes as possible before they reform and repeat the cycle until the boss dies.
Fryguy from Super Mario Bros. 2. Hit him with mushroom blocks three times, and he splits into four smaller Fryguys, which only take one mushroom block hit each to kill. Of course, with each mini-Fryguy you kill, the others get faster, making the last one far more dangerous than even the original big one. On top of that, some versions of the cartridge have a glitch that can leave the fight unwinnable if you get hit by one of the pieces while taking out another.
The Phantamanta monster in Super Mario Sunshine probably takes the cake for number of "little asteroids". It splits 6 times to make 128 tiny manta ray ghosties—each split divides them up into 2 smaller ones except for the last, which splits them into 4.
The green Cerberus-like creatures in God of War. They spit out nasty little puppies called Cerberus Seeds which, if left alive long enough, would grow into full-sized Cerberi, which will eventually spit out more Seeds... One area of the first game is deliberately set up so you have to kill a number of them before they multiply too much.
Boss Boom Box in Banjo-Kazooie is a boss example. A mook example is the ice cubes found in Freezeezy Peak and the winter version of Click Clock Wood.
A rare non-enemy example can be found in a Dummied Out item in the Gamecube version of Animal Crossing, the paper airplane. Dropping it outside places a little paper airplane on the ground, but exiting and entering a building causes them to multiply. They will eventually spread like wildfire, locking up the whole acre, and if it continues, your whole town! And don't bother trying to pick them up, they'll appear to be gone, but they are still there and will come back, complete with multiplying, when you enter and exit again.
The Promethean in Age of Mythology is a clay dwarf that splits into two smaller ones when killed (the two minis die normally). In one of the scenarios, the Titan Prometheus is capable of generating the large ones intentionally by scraping clay from his arms.
Inverted in Final Fantasy IV with the Calcobrena, a group of trick bosses consisting of six small dolls with a small amount of HP... except that if you kill them in the wrong order, the remainder turn into a giant doll that's a lot tougher to kill.
Also appearing in the game is the Mom Bomb, which grows into a massive monster, then explodes, damaging you and leaving a bunch of smaller bombs in its place.
Also appears in Final Fantasy III, with splitting monsters in two dungeons. Fortunately, you can stop them from splitting. Unfortunately, only by rapidly burning through your limited spell charges or by using the others far less than useful Magic Knight class to kill them with katana.
Final Fantasy VII has some nesting doll-like enemies near Costa Del Sol that spit out a smaller version of itself when killed. They are pathetically easy to kill.
Inverted in later Dragon Quest games. In a random encounter of eight ordinary-looking Slimes, if they all survive a turn they pile together to form a King Slime.
In City of Heroes, several Devouring Earth baddies leave smaller versions behind at death, though they usually don't split any further. Some high-ranking Clockwork pull this as well.
The Giant Monster versions of the Devouring Earth rock and crystal enemies actually split into upwards of four or five normal-sized enemies, which can then further split into the smallest versions.
Several of the GUILT in Trauma Center: Under The Knife/Second Opinion. One is Paraskevi, a worm thing that instantly kills the patient if you let it live too long, and the only way to kill it is to stun it with the laser then cut it in half, then cut those pieces in half, and so on, until you can remove the little pieces. The other is Savato, which can create little baby versions of itself that can grow into semi-savatos if you aren't careful.
The King of Shadows, the final boss of Neverwinter Nights 2. First, you defeat him normally, then he splits into smaller copies, and after you defeat them, he reassembles and becomes a Puzzle Boss.
In Castlevania III: Dracula's Curse, the Phantom Bat boss splits into smaller bats when hit. Only after reducing them to the smallest size could they be defeated. Super Castlevania IV had a few random encounters that worked this way, as well as the Zapf Bat boss, which did the same thing.
Castlevania: Harmony of Dissonance has a slime boss that breaks down into smaller slimes every time it is hit (with each slime then acting as an individual enemy). These divisions are much weaker than the boss, and they also result in the boss becoming smaller and smaller. In other words, the fight becomes easier as it goes.
World of Warcraft has a few cases of rock giants that will fracture into smaller rock giants, but there will always be the main "piece" and then smaller "shards". The main rock giant can be defeated before or after you defeat its shards. Thankfully, though the main rock giant is an extra powerful elite monster, his shardlings are normal powered or slightly underpowered for their level.
Additionally, hydras from Warcraft III split into smaller hydras to simulate head regeneration. Slime beasts do the same, with one particularly big one in the Orc expansion campaign splitting about 10 times, each split splitting into two smaller ones.
There's a variation with a water elemental in the Violet Hold instance. "She" will explode into numerous smaller elementals periodically throughout the fight. "She" can't be damaged except by destroying the smaller entities before they can rejoin the main body.
One of the bosses in the Halls of Origination instance from Cataclysm is guarded by fire elementals that each split into two smaller elementals when killed, who each split into two even smaller, who each split into two more. Kill them one split at a time or you'll quickly get surrounded by Goddamned Bats. You used to be able to prevent the splitting by using a stun ability at the right time, but this has been addressed in a patch.
The Doom series features the Pain Elemental. Kill it, and it splits into three Lost Souls. (Don't kill it, and it spits Lost Souls one by one. Hard to be sure which is worse.)
In the Doom II RPG for cellphones, the Spider Mastermind will break into three Arachnotrons. This is actually the hardest part of the fight since the Arachnotrons are quite fast, and you're probably running low on health and all those Nano Drinks you used at the start of the fight have worn off.
The appropriately-named asteroids in Geometry Wars Galaxies levels whose names start with Mas- or Por- will split in half, then the halves will release 5-10 monsters of the same shape when destroyed. Also, the spinners are a mild example. The big ones split into two smaller ones, the two smaller ones die normally.
In Desktop Tower Defense, the "spawn" critters divide into two smaller ones, and the two smaller ones are then killed normally.
NES The Addams Family video game Fester's Quest includes green slimeballs that multiply when shot... The problem is that they don't split up into a set amount like most enemies of this type and will continue to multiply over and over again no matter what. Without large weapon upgrades or explosives, the slimes will continually regenerate until you are able to quickly destroy every single last one. On the upside, they leave lots of powerups upon their deaths. On the downside, the game includes power downs, and the leave those too, leaving you to figure out how to get the good stuff while not losing the powerups you already got.
Variation of this in Parasite Eve. In the game's Bonus Dungeon, there's a giant cockroach boss that can lay a larva. If the larva isn't killed fast enough, it will reach adulthood and gain the same stats and abilities of its parent, including the ability to lay another larva. This means that the fight can loop indefinitely unless you break the cycle.
The mutated scorpion boss plays this trope straight. After you've dealt enough damage to the boss, it splits into 4 parts, boxes you in the center of the battlefield in by encircling you, and attacks one at a time.
Not so dangerous is a monster in the regular game that spawns brains that then detach and bounce around. Kill enough to bump the battle's target counter to 99 and you can earn a Super Tool.
Star Fox often has literal asteroids that behave this way. While not explicitly enemies, some games in the series treat them as such, allowing the player to get extra kills by destroying them.
Command, while not having splitting asteroids, has minor enemies that act this way.
A type of Met in Mega Man 5. Upside, they can give multiple powerups. Downside, they bounce, making them hard to hit.
The lava golems in Serious Sam. And not only once, but the smaller fragments divide into smaller fragments when they die, and those smaller fragments divide into even smaller fragments.
The Fission Metroids in Metroid Prime, though they only divide once.
Metroid Prime 3 has the Phazites, floating balls of semi-sentient Phazon that show up once you beat the boss of a planet. Very annoying since it takes going into Hypermode to kill them, which both uses a tank of energy and puts Samus at risk of a Non-Standard Game Over.
Metroid: Fusion inverts this, where the X-Parasites dropped by killed enemies, if left alone long enough, will either reform into the exact same monster they had been, or seek out another one to make it grow bigger.
Some forms of Artificial Chaos in Sonic Adventure 2 (and all of them in Shadow the Hedgehog) are of the re-forming variety; to destroy them you have to break them apart and destroy the smaller ones, then attack the core, but if you don't destroy the small ones quickly enough, they reattach to the core.
The black pudding monsters in Nethack divide when they're hit with a non-lethal blow (with a weapon which is made out of iron), rather than when they die. Each of the child puddings are the same size as the original, but only have as much health as the parent did after taking damage from the blow, so hitting them with high damage blows will reduce the number of times they divide. On the other hand, if you hit them with a underpowered weapon which does a minimum of damage and occasionally give them a rest so they can heal you can "pudding farm" an endless amount of them, giving you countless pudding corpses to sacrifice to your god and, since monsters sometimes Randomly Drop items, and endless supply of items.
Similar hijinks can be done in Elona with bubbles, and with high fire resist, believers of fire (summon other fire creatures when in melee), although the Goddamned Bats interpretation of the trope arises with Aliens (impregnate rather than split, the child taking the stats of the parent NPC), Mass Monsters (Semi-strong rocklike monsters whose chief way of killing is stat draining), and finally the almighty Machine Cube, which is like the borg version of a D&D Gelatinous Ochre cube.
The antwerp in Quest For Glory 1 splits into several smaller antwerps if you use your sword on it when it jumps on you. Borderline case, since only the original is hostile.
The larger rocks in the Intellivision game Astrosmash would split into two smaller rocks when shot.
Will Rock has the Minotaurs. When killed, they are blown to bloody bits, which quickly regenerate into two smaller, weaker, but also more aggressive Blood Minotaurs. Thankfully, you later acquire some weapons which can destroy them in a single shot, preventing the splitting.
The Pang series of games have five different sizes of balloons as enemies. Hitting a balloon of any size except the smallest will cause it to split into two (or sometimes four) of the next smallest size.
Ape Escape has a certain jumping enemy. If the smallest size enemy touches you, it hurts you and dies.
Flash game Medieval Rampage has large ice golems which split into two or three fast but weaker ones. Actually one of the weaker enemies though since the large version is so slow you can blast him at your leisure, and the small ones die with one or two shots. Good to farm.
Cut off the tentacles of a Reynaldo in Onimusha, and the severed appendage will grow into a new Reynaldo if left alone long enough.
In the Descent games, the Sidearms and Spiders do this, and the offspring tend to be Goddamned Bats or Demonic Spiders. The Sidearm Modulas can also reform into full-size Sidearms, similar to the aformentioned Floormasters. Other enemies will also sometimes do this, eg producing Internal Tactical Droids or Red Hornets.
Slimes in Rogue.
In the first Kingdom Hearts, Atlantica had an enemy called Sheltering Zone which would split into five or six Sea Neons, the undersea equivalent of a Shadow. Kingdom Hearts: Birth by Sleep adds the Blobmob, a jellyfish-looking Unversed found only in the Deep Space world that when killed would split into two... and each of those two would split into two mored when killed. Repeat once more for a total of seven kills from one enemy.
The Clutter will split into 1-3 baby versions of itself if defeated, each of which can grow into an adult sized one. Thankfully, they cannot kill the player character.
The Amalgam is a far more dangerous one — hitting it when it is too large will cause it to break apart into smaller pieces. Each smaller Amalgam can absorb more slimes wandering about, causing them to grow big again. Oh, and if you touch a large enough Amalgam, you are absorbed (read: you die) on the spot.
Some monsters in the Avernum series (particularly slimes) split every time it's their turn, but only if you damaged them in the time between their current turn and the last turn. Rather than being smaller and weaker, each duplicate has the same power as the original—but they also have the same post-damage HP (so if you hit one for 10 damage, the duplicate will also have 10 damage on its count.) It's best to only attack one per turn, but hit that one with everything you've got.
The Exile games had the same mechanic. In Exile III, for instance, it was used twice - once on a fairly weak low-level slime, and once on the doomguard, which had 150 hit points and was a mid-level boss by itself.
Exile and Avernum both take their cues from the Ultima series, especially Ultima V; slimes and gargoyles in Ultima V divide when struck, assuming that they're not killed on the first blow. Slimes only appear in groups of sixteen, and each will divide once; there are subtle visual differences between divided and undivided slimes.
Asteroids Deluxe had the asteroids, duh, but also Killer Satellites where the pieces also home in on your ship.
Slimes in Minecraft come in four sizes, which can withstand and deal proportional amounts of damage. Killing a slime will cause a it to split into four of the next size down. The smallest size slime will still chase you around but can't hurt you (unless it pushes you off a ledge or into lava).
In the official release (1.0), creatures in the Nether called Magma Cubes do this as well. And much like the smallest slimes, the small magma cubes are ADORABLE!
Starfish enemies in Bug!, as well as a brown beetle enemy (for some inexplicable reason).
Each episode of Major Stryker has a boss that does this for its second phase.
Terraria has mother slimes which split into baby slimes on death.
The King Slime produces Blue Slimes whenever you hit it, implying that you're cutting little bits and pieces of it off.
There's also the Eater of Worlds, which is basically the Centipede converted into a platformer boss.
X-Com: Apocalypse alien Multiworm releases four Hyperworms when killed.
Spiral Knights actually inverts this. There is a type of slime that alone is very weak and easily defeated. However, groups can quickly merge together into a single enormous, very powerful slime monster.
One of Stewie's levels in Family Guy Video Game! takes place in Peter's brain, where there are memories of Lois who can kill him with their attempts to hug him. If they're attacked, they multiply into clones dressed in one of her outfits from the show and also attack by throwing objects corresponding to that outfit. The first batch of clones in turn multiply into two more when defeated.
One of the enemies in Zanac was an egg that would come a third of the way into the screen, and, unless it was shot down first, split in half, releasing its payload. The two half-shells were much harder to destroy than the egg. This enemy actually first appeared in E.I., Compile's very first Shoot 'em Up.
Gravity Crash has the indigenous squid-like lifeforms that split into 5 smaller squids when hit.
A lot of enemies in The Binding of Isaac split into smaller parts when hit. For normal enemies, some flies, brains . For bosses, Envy, Blastocyst and Fistula break up into smaller parts upon destruction. Some also spawn several different enemies upon death like the Duke of Flies.
The Stingray from Mini Robot Wars splits into three weak copies when destroyed. Much more of a nuisance if anything, as neither the large or small stingrays could attack.
In Zeliard, hitting red slimes with basic weapons or spells would make them multiply, and not even damage them.
The Entrails Parasite boss in Tales of Graces splits into eight smaller versions of itself after it takes a bit of damage. On higher difficulties, they can be extremely troublesome to deal with, as they cast spells rapidly, and can KO the entire party in seconds if they're not interrupted with area attacks.
Subverted in LEGO Rock Raiders for the PC. Blasting apart a rock or ice monster with a laser beam (or a lava monster with a freezer beam) causes it to spawn three knee-high versions of itself ... which then make a run for the nearest wall and dig their way to safety.
In the video game adaptation of Gremlins 2: The New Batch, giant spider enemies will split into three smaller spiders upon death.
Mizar of Devil Survivor 2 is one of these, with the added complication that the blobs grow and split all on their own, meaning that it can replicate indefinitely if not finished off quickly. Unfortunately, it's already grown well past that point before you even find out it exists...
Happy Tree Friends: Overlapping with Me's a Crowd, in the episode "Peas in a Pod" Lumpy unknowingly plants an alien seed coming from a fallen comet, which becomes a large stalk that spews out a green pod clone of the light blue moose. Being Lumpy, he uses the clone to manage his chores. The somehow more dimwitted clone ends up accidentally chopping off its own leg during wood cutting, which regenerates and becomes another Lumpy clone. Realizing he will have more clones to manage his chores, Lumpy chops up the pod Lumpies until he has an entire army of Lumpy clones willing to do his bidding. Of course the clones cause havoc by killing the other characters whom they mistake for things Lumpy wanted cleaned (such as wiping Sniffles' face so hard his brain is exposed or crushing Cuddles with a mop). The entire episode is a parody of Invasion of the Body Snatchers.
In an episode of ReBoot, the heroes (who have become characters in a dungeon-crawler) are attacked by two animated suits of armor. Dot casts a spell that ends up splitting them into four suits that are half the size. Dot casts the spell several times over, then Bob and Enzo start stomping.
In the "Sorcerer's Apprentice" sequence in Fantasia, Mickey Mouse enchants a broom to fetch water in his place. When he realizes that it won't stop and he doesn't know how to enchant it to stop, Mickey chops the broom into pieces with an axe. A minute later, the splinters turn into hundreds of brooms that won't stop, and poor Mickey finds himself in over his head.
This is direct from Goethe's poem Die Zauberlehrling, although that particular apprentice only cuts the broom in half and only has to deal with two.
Taken Up to Eleven in an episode of The Simpsons that spoofs the Sorcerer's Apprentice - Scratchtasia. Scratchy keeps cutting Itchy into pieces only to have each piece become a smaller copy. In exasperation, Scratchy rapidly cuts them until nothing is left but powder. He then sighs, inhaling the powder, which becomes powder-sized versions of Itchy that kill him from the inside out.
Samurai Jack Aku has demonstrated the ability to split into multiple copies of himself when struck.
Jack also took on one of these monsters in the beginning of another episode, capped off with a "WHO ELSE WANTS SOME!?!".
Still only have two eyes and one tooth between all of them though. They also seemed to get dumber (if you can even tell) and their voices got higher the smaller they were. Plus, Shake KNEW they just kept getting more annoying, but couldn't help himself from cutting them up into smaller pieces for fun.
The space-based Rock Lords in Transformers Animated have this ability. Unfortunately, it only works once, and it didn't do the one who swallowed Bumblebee much good when it went up against Sari.
A series of shorts on Nickelodeon had a pair of Ineffectual Villain alien invaders who landed on a planet inhabited by a little alien that split into two more when they first tried to zap it with their laser guns. They took advantage of the alien's ability by zapping it numerous times, making more little aliens happily willing to serve their every need. Things go out of hand (as they always do for them) when too many zaps causes too many little aliens running around, which makes the pair zap them even more, which of course makes even more of them. Eventually they're forced to leave the planet as it overflows with little aliens.
SpongeBob SquarePants: Patrick Star, being a fat pink starfish, demonstrated this in at least one episode.
Taz-Mania: When Taz blows up the eponymous thing in "The Thing That Ate the Outback", he finds himself facing an army of miniature things; each one as ravenous as the original.
Generator Rex: In the episode "Mixed Signals," Rex slices the Starfish E.V.O in half not knowing about it's ability to divide thus causing to continually divide into smaller and smaller units making it even harder to catch. Rex and co finally manage to subdue it after the creature is injected with a serum causing it to reassemble into its complete form.
Many simple-bodied organisms can reproduce asexually by splitting into smaller fragments. The planaria in particular is renowned for its regenerative capabilities: an individual can be cut into as many as eight equal pieces, each of which can survive and develop into a separate planaria.
Cut an arm off a starfish, and not only will the starfish grow another arm, the arm will grow another starfish.
Can be a big problem in weed control. Mowing or stomping or pummeling may kill the original plant or fungus, but the act of destruction will spread the seeds or spores around a wide area causing the problem to get worse. Many invasive weeds can resprout from cuttings and root fragments as well.
If you smash a spider that's carrying an egg sack, there's a chance you'll end up with a lot of little spiders.
Often a problem when dealing with Organized Crime or Terrorist networks. Killing the leader doesn't simply cause his followers to give up and go home; instead, they fight to fill the power vacuum, becoming fragmented and generally more violent in the process. So instead of dealing with one well-disciplined organization, law enforcement suddenly has to deal with countless autonomous organizations.
This effect has been observed in both the Mexican and Colombian drug cartels after major Drug Lords were killed or arrested and with Al-Qaeda after their leadership was killed and dispersed.