Lucky you, you just bought a new pet at The Little Shop That Wasn't There Yesterday. But you'd better be sure that you read the care-of manual very carefully. Odds are there is one thing that your pet should never under any circumstances get its hands on, otherwise it'll start growing... and growing... and growing, until it's a 50-Foot Whatever. Before you know it, the military will be shooting at your pet, unaware that all it needs is some Applied Phlebotinum to get back to normal. This may be a natural part of the creature's biology, or it could be the creature became exposed to Green Rocks. When a villain does this deliberately, it's Make My Monster Grow.
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Anime & Manga
- Moguchan, from an episode of Mirumo De Pon, a plushie brought to life by Rirumu's magic, grew whenever it ate anything.
- In the second-to-last episode of Wandaba Style, Michael Hanagata becomes enamored of Sachiko, a tentacle alien that gets bigger when exposed to water. Unfortunately, Michael takes her to play in the ocean...
- Demashita! Powerpuff Girls Z has an episode where a duck grows bigger.
- Love Hina has an episode where a robot turtle grows bigger the more metal it eats.
- The last episode of FLCL has Mamimi feed a robot dog, which grows.
- Rage Shenron from Dragon Ball GT grows bigger the more electricity he absorbs.
- In one episode of Wedding Peach, the Love Angels fight a snow demon that grows every time Angel Salvia cuts it with her sword.
- Happens to Nega (a tiny extra-terrestrial cat) when he is infected by Earth's common-cold virus, in the gag episode "The 'atchoo!' of horrors" of Magical Angel Creamy Mami.
- One Donald Duck comic had Donald bringing a special African snail to eat the crab grass on Uncle Scrooge's lawn (which Donald had caused by buying cheap lawn seed). What he didn't realise was that the snail would keep growing as long as it had a steady source of food.
Films — Live-Action
- Honey, I Blew Up the Kid had a human baby who grew bigger whenever it was exposed to electricity.
- The Blob (1958): The Blob gets larger the more it eats.
- Hedorah from Godzilla vs. the Smog Monster grows larger and more powerful the more it eats toxic waste.
- Evolution: The aliens react to fire by melding and enlarging. So when the Army decides to napalm-bomb them... they cause one singular cell to rapidly evolve into a simple, gigantic amoeba that wipes out a substantial amount of the military before it's de-evolved due to chemicals in shampoo.
- The Crites from the Critters film series grow after they eat.
- In 7 Faces of Dr. Lao, it turns out that Dr. Lao's pet goldfish has this problem if any part of it is exposed to air. When the Mooks of the Big Bad knock over the goldfish's little bowl, it grows... into the Loch Ness Monster.
- 20 Million Miles to Earth features a wonderful Harryhausen creature that grows uncontrollably because of Earth's oxygen rich atmosphere.
- The eponymous Kaiju of Pulgasari grows from a tiny figurine size to Godzilla size as it eats more iron. After figuring this out and also realizing that Pulgasari is invincible, the peasant rebels start going out of their way to feed it all the enemy weapons they can get their hands on.
- The classic children's book A Fish Out of Water.
- Monster Blood from the Goosebumps subseries of the same name, along with whoever or whatever eats some.
- In the story "The Baker's Cat" by Joan Aiken, a cat grows larger than the entire town after his owner feeds him yeast.
- In the children's book There's No Such Thing as a Dragon, Billy's mom's denial of the dragon's existence causes it to continually grow larger.
- Kitten Kong from The Goodies, who ate feed laced with growth hormone and started growing a lot.
- The Chicken Heart probably fits here... it's not a WHOLE creature, but it still grows... and grows... and grows... until it is as big as Earth.
- Green slime from early editions of Dungeons & Dragons worked like this, dripping onto organic materials and converting them into more slime. Careless adventurers in the early days of role-playing sometimes accidentally caused entire dungeons to fill up with the stuff.
- Audrey II from Little Shop of Horrors. The more blood it gets, the bigger it gets.
- The Maw, from the Xbox Live Arcade game of the same name. He ends up swallowing the entire planet the game took place on.
- The Munchables for the Wii. Both player characters do this, but shrink back to normal at the end of every level when they...turn everything they ate into orbs.
- In Wallace & Gromit's Grand Adventures: Fright of the Bumblebees, Wallace makes flowers grow to absurd proportions by a homemade fertilizer he creates out of the active ingredients of body-builder's weight gain formula, then the bees who who are fed pollen from the flowers grow to enormous size, with the queen ending up the size of his truck. One has to wonder if there were any side effects from eating the honey that the bees produced...
- While he's already pretty competent in the combat area, Little Birdie from Metroid: Other M later becomes a bizarre, furry scorpion-dinosaur, then a space dragon. Yes, that space dragon. Joker Immunity at it's finest.
- A Wii-exclusive powerup in Sonic Colors involves becoming one of these.
- The titular blob in Tales from Space: About a Blob is one of these. It shrinks back down twice, but on it's third try, it grows bigger than the planet.
- In the various Ivalice Alliance games, the Carrot is an escaped pet that when the party encounters it turns out to have mutated into a massive malboro, a recurring creature in the Final Fantasy games known for its ability to inflict multiple status ailments.
- Tasty Planet and all the 50 other similar games.
- In Fallout 3, the Vault 87 strain of Super Mutants continually increase in size with age, eventually becoming 2-story tall Behemoths.
- In the intro of Blaster Master, Jason's pet frog Fred grows to enormous size after jumping on a radioactive container, and in the game he becomes the boss of Area 4 and 7.
- The Wow! Wow! Wubbzy! episode "Attack of the 50-Foot Fleegle": Wubbzy's new pet is never supposed to be fed candy, specifically because of this trope.
- Beebo from The Powerpuff Girls was designed to be fed only once in his lifetime, but the girls ended up feeding it once each. It ends up eating half the town.
- A hamster during an Invader Zim episode gets larger and larger the more it eats.
- Viva Pinata episode "Confetti-itis" has this happen to most characters in the show.
- Tank on Lilo & Stitch: The Series has this happen to him the more he eats.
- The Courage the Cowardly Dog episode "Muriel Blows Up" has this happen to each of the main characters.
- Happens to a little alien felon whom Guy Gardner douses with coffee in the Cold Open of one episode of Batman: The Brave and the Bold.
- Eileen a.k.a. "Birthday Girl" on WordGirl gets bigger (and greener) the greedier she gets.
- The sponge monster from the My Life as a Teenage Robot episode "Speak No Evil" grew every time it was exposed to water.
- Johnny Test also had a sponge monster that grew when it was exposed to water.
- Veggie Tales:
- A monster representing a lie Junior Asparagus told keeps getting bigger as Junior has to tell bigger and bigger lies in order to cover up the first lie he made.
- There was a similar episode in which a "Rumor Weed" grew and eventually took over the town as a rumor spread and became more and more exaggerated.
- In one Sushi Pack episode, a scientist creates a tiny dinosaur that eats trash. It accidentally gets splashed with chemicals, which makes it grow bit by bit with all the trash it eats. It also somehow gains the ability to turn anything into trash for it to eat.
- Jimmy Two-Shoes: Yet another fine product from Misery Inc. Useful for a Clingy Jealous Girl needing to break up an alleged date her crush is on.
- In The Grim Adventures of Billy & Mandy episode "Little Rock of Horrors", this happens to a Meteor that falls out of a sky that eats brains.
- An episode of Chip 'n Dale Rescue Rangers has Dale adopting an alien lizard that appears to play the trope straight at first, before revealing that he is just as intelligent as the main characters. However, he loses intelligence at the same time as he gains size, and it's stated that the ancient dinosaurs were the result of a previous away team succumbing to this fate.
- Jackie Chan Adventures had Hak Fu summoning miniature shadowkhan. They failed to prove a threat until he discovered their shadow-eating abilities. It rendered victims comatose and turned them into massive landsharks.
- In the My Little Pony: Friendship Is Magic episode "Secret of My Excess", Spike becomes bigger and bigger the greedier he gets.
- The Mongolian Fire Fist Demon from the Kung Fu Panda Legends Of Awesomeness episode "Po Fans Out", which gets bigger whenever it gets hit.
- A once-off Mad Scientist villain in The Atom Ant Show creates a "Gobbling Glob", a small gelatinous monster (looking something like a Pac-Man ghost) which is only the size of a baseball... but grows bigger and bigger as it eats. And it's ravenously hungry...
- The Adventure Time episode "Dungeon" has Finn facing the Bucket Knight. He starts out small, but grows huge by pouring a bucket of water over himself.
Bucket Knight: Just... add... water!
- In Wakfu, Rubilax grows larger each time he is attacked. Sadlygrove is able to defeat him by attacking him until he sinks into the ground.