A deserted island which is not-so deserted. Somewhere on the island is a horrific giant beast. The telltale signs that it's there are usually giant footprints in the sand along the beach, the rumbling of footsteps or the clattering of trees being knocked down, and of course, a horrifying roar.
Usually, these types of creatures are the island's dominant species or ruler, lording over the place because they are the biggest and strongest. In some cases though, they are guardians protecting something residing on the island. Of course, there's also the possibility that the creature is trapped on the island, being surrounded by water on all sides makes it a good prison, in the event the creature cannot swim or is weak against water.
The type of creature that is usually the island's inhabitant can range from creatures from prehistoric times to everyday animals of the giant variety, especially crabs, spiders, and insects. Eldritch or Animalistic Abominations are not excluded from this. In some cases, the island can even be a domain of Mechanical Monsters. Of course, the visitor of the island might not even see what the beast is, due to perhaps being an Invisible Monster or perhaps just to invoke Nothing Is Scarier.
Can be an Island of Mystery if those that land are unaware of the creature residing on it at first. Usually used in a Trapped with Monster Plot, especially if the island's visitors are marooned. Different from Turtle Island, which is where an island is a creature, although it is not impossible that the moving island has a beast imprisoned on it. Similar to Beast in the Maze where a creature resides in a labyrinth instead of an island. If there is more than just one giant beast on the island, a Behemoth Battle is likely to happen between them. If the creature has a large stash of treasure, that is a Dragon Hoard. For a wider variety of monster dwellings, see Home of Monsters.
- After surviving the sinking of the St. Anne, Ash's party and Team Rocket end up stuck on an island made up of malfunctioning giant animatronic Pokémon, separated from their Pokémon.
- Another episode during the OI season has Meowth and Pikachu tied together in the middle of Fairchild Island, an island containing giant Rhydon and Pidgeot who attack anyone that comes near.
- An issue of Planetary that's a homage to the Godzilla films has the team exploring an island somewhere in the vicinity of Japan that is home to a variety of giant prehistoric monsters, all of which have supposedly died out. Emphasis on supposedly.
- The Centre from DC: The New Frontier, a Hive Mind of prehistoric beasts.
- Mossflower Odyssey 3 takes place on an island inhabited by giant snakes, deadly natives, and is guarded by a Ghost Ship.
- Jurassic Park is an abandoned dinosaur theme park on a tropical island, inhabited by reanimated dinosaurs.
- King Kong: Skull Island is an island teaming with horrific beasts and dinosaurs, with the titular giant ape reigning as king of them.
- In Kong: Skull Island, it's revealed that Skull Island is actually located on top of a rip in the Earth's crust where giant monsters (such as the reptilian "Skullcrawlers"), are able to emerge from Beneath the Earth.
- The famous Godzilla film series gives us Monster Island, which as its name suggests, is home to many of the kaiju that appear in the films, including the titular King of the Monsters.
- Mysterious Island is about a group of castaways who find an island populated by giant animals like crabs, chickens and bees. They were all the work of Captain Nemo as a solution to world hunger.
- At the end of Deep Rising, the remaining survivors have escaped to a beautiful sunlit island, only to hear a terrifying monster roar. The camera pulls back to reveal the island is host to an erupting volcano and something tearing down trees as it makes a beeline for the beach where the protagonists are. Cut to credits as the hero asks with exasperation, "NOW what?"
- In Jason and the Argonauts, while on the Isle of Bronze, Hercules inadvertently awakens the Living Statue of Talos when he steals from the crypt he was guarding. Though the Argonauts manage to defeat Talos, Hercules' best friend Hylas was killed during the battle.
- The island of Colossa from The 7th Voyage of Sinbad, which is populated by cyclopes, rocs, and dragons.
- Jules Verne's Mystery on Monster Island: It's an island of monsters. Not really. The hero's uncle manufactured them to give his nephew an adventure.
- Played with in Lord of the Flies. Most of the boys think there is a physical beast and by the end of the book start to almost worship it, but there is no "real" beast. The idea of the beast is actually used to represent of humanity's innate evil.
- The Ur-Example is The Odyssey, where Odysseus and his crew dock on an island inhabited by a Cyclops named Polyphemus, who imprisons them in his cave and eats them two by two. They defeat the monster by stabbing his eye out with a stick.
- The title character of Sinbad the Sailor often ends up on one of these during his travels, including one where a Roc bird nests, and another inhabited by a man-eating giant (who's basically an Expy of Polyphemus from The Odyssey and gets defeated in a similar manner).
- Fragment: Henders Island is a remnant of an ancient supercontinent from the Precambrian era, where everything has been evolving separately for 570 million years and the inherent savagery of life has been turned up to eleven; an orgy of violence where the food chain is thrown out the window and everything eats everything - the dominant lifeform being a land-going species of mantis shrimp capable of single-hand(claw?)edly shredding and devouring tanks.
- The Ultra Series has featured a couple over the years.
- One of the first and best-known episodes of the original Ultraman was "The Lawless Monster Zone", in which the Science Patrol visits an island populated by various giant monsters like the dinosaur-like Red King, the bat-like Chandler, and a giant burrowing reptile called Magular. Another one appeared in their Multi-Part Episode, this time home to relic dinosaur and Ensemble Dark Horse of the franchise Gomora.
- In Ultraman 80, UGM finds an abandoned island resort where an evil alien monster called Gimyra has hypnotized everyone on the island to drink their blood and turn them into its giant monster minions.
- In one episode of Ultraman Dyna, Super GUTS visits an island populated by several monsters they have previously met. It soon turns out that the creatures are clones being used as practice targets for a Mad Scientist-made monster called Neosaurus.
- Subverted with the Kapuya Islands of Ultraman Cosmos. While the archipelago hosts a variety of kaiju, the place is meant to be a sanctuary for them, having been created by EYES as a home for monsters subdued by Cosmos. Besides, most of the creatures on the island are Gentle Giants like the Giant Flyer Lidorias, the mole-like Mogrudon, and the energy-eating reptile Bolgils.
- Ultraman Max homaged the original example in a two-part episode featuring Red King, as well as two new monsters — a giant newt called Salamandon and a gliding reptile called Paragler. It's later revealed that the island is actually a dimension-hopping prison for Red King built by Atlantis, and the other two monsters are its guards.
- Ultra Galaxy Mega Monster Battle takes it Up to Eleven with Bolis, an entire planet of giant horrors. Naturally, the story is that the main characters are stranded on the world in a space expedition and have to survive all the kaiju (all pulled from previous series) that do nothing but attack anything they see.
- In one episode of Hannah-Barbara's cartoon adaption of of The Godzilla Power Hour, appropriately titled "The Horror of Forgotten Island", the crew of the Calico found themselves on an island surrounded by a force field which imprisoned a mutant cyclops that could turn invisible.
- The Simpsons subverted this in an Imagine Spot. When Lisa is told she's failing gym in one episode, she imagines that it costs her a government position and she's sent to "Monster Island". She's told "It's just a name", but ends up getting chased by monsters anyway.
Lisa: I thought it was just a name!
Man: What he meant was that Monster Island is actually a peninsula.
- Steven Universe: Mask Island is not only the home of the beastly Invisible Gem Monster, but was also the battlefield for Malachite.
- In Popeye the Sailor Meets Sindbad the Sailor, Sindbad lives on a Turtle Island where he keeps many dangerous beasts as pets, such as lions, tigers, snakes, apes, a roc bird and a two-headed giant.
- As a Shout-Out to King Kong, in an episode of Nelvana's Babar animated series titled "Conga the Terrible", the young elephant king and his friends get shipwrecked on an island that's home of a giant Killer Gorilla that dwarfs even the elephants. In a subversion, the gorilla turns out to be quite friendly once they get on his good side.
- There is a Monster Island in The Powerpuff Girls, source of all the Kaiju that attack Townsville from time to time. Turns out they do it for the honor of fighting the Girls.
- In Godzilla: The Series, Monster Island is where the military keeps all monsters that have been captured over the course of the series (barring those that need a Tailor-Made Prison instead).
- Several appeared in Jonny Quest, with the beasts that inhabited them usually the result of a Mad Scientist.
- In the DuckTales (1987) episode "Raiders of the Lost Harp", when Scrooge discovers the lost city of Troy and the eponymous harp, the Minotaur statue that was guarding it comes to life and follows Scrooge all the way to Duckberg to get it back.
- Adventure Time: In "Mysterious Island", the island is full of giant version of various animals, most of which are hostile.
- Island Gigantism, as Wikipedia states, is "a biological phenomenon in which the size of animals isolated on an island increases dramatically in comparison to their mainland relatives." Results in things like the Komodo Dragon (probably the closest thing to a Real Life example of this trope), the Madagascar Elephant Bird (a flightless bird twice the size of an ostrich), and the Giant Tortoise of the Galápagos.
- Inverted with insular dwarfism, in which large animals become smaller due to the limited resources available. This has occurred with elephants, hippopotamuses, dinosaurs, and even a species of prehistoric human. Such creatures can often be found in the same environment as examples of the phenomenon's opposite.