Gwoemul

The Monster is an unnamed fish-like mutant and the main antagonist of the 2006 South Korean monster film, The Host.

Despite not talking, its vocal sounds are provided by Oh Dal-su.

Appearance
The monster has a tadpole-like design with a massive mouth that can open in flaps surrounded in teeth, gills, two eyes, and arms with two small feet located directly behind the arms. It can use its fin tail not only for support while swimming, but also for support while climbing and grabbing prey. It also has a few fish stuck on its back to show its mutational side.

Biology
Similar to an amphibian, the monster can both breathe air through its lungs and gills. It traps humans in its mouth and regurgitates their bodies out into a moist encloser to consume them later. It also licks its tongue on the spat out bodies to make sure they are dead. After its prey is fully consumed, it vomits out their bones as it is unable to decompose the skeleton.

History
The monster's origins are brief, yet understandable. In late 2000, an American military pathologist and his Korean assistant dump 200 bottles of formaldehyde down a drain leading to the Han River near Seoul. Over the years, there are sightings of an amphibious creature in the water, fish in the river begin dying off, and a suicidal man spots something moving in the water before jumping from a bridge.

One day, as Park Gang-do, a man who runs a snack shop in a park near the Han River along with his father Hee-bong, delivers food to customers, he and several others spot a dark figure in the water of the river. The people begin throwing cans into the river to scare it off, but are attacked by a creature that emerges from the river and runs loose throughout the city, eating several people whole and injuring many others. Gang-do spots his daughter, Hyun-seo, in the crowd and grabs her, but only after tripping he realizes he grabbed a different girl, before witnessing the monster grab Hyun-seo with its tail and diving back into the river. Gang-do and his family are taken to a hospital by American military officers, as the monster is believed to be a host to a deadly virus.

Meanwhile in a small section of the sewer, the monster regurges several of its victims in a hole to consume them later, including Hyun-seo, who hides from the monster's sight in a small pipe opening. Gang-do, learning that his daughter is still alive via phone call, escapes from the hospital with his father and siblings, Nam-il and Nam-joo, to track the monsters location. Two homeless boys are swallowed by the monster that night and Hyun-seo helps the only regurged survivor, Se-joo, into the pipe with her.

The family discovers the monster wandering about next morning from within their snack shop and shoot at it, only aggravating it enough to tip the entire shack on its side. Hee-bong allows himself to be killed by the monster to let his kids escape from the beast. The siblings are then taken back to the hospital, where they eavesdrop on scientists discussing that there was no virus, only a myth made up to hide the creature's origins. With the help of a homeless man who is also in the hospital, the three are able to escape.

Back in the sewers, as the monster vomits out the skeletal remains of its prey, it attacks Hyun-seo and Se-joo when the latter starts to cry, but is unable to reach them through the pipe. As it rests, the two kids make a rope out of the victims' clothing to escape from the hole, but realize too late that the monster only pretended to be asleep to lure them out of their hiding spot, and are swallowed up by the monster before they are able to return to said hiding spot.

Gang-do finds the monster's hiding spot to find it empty. While investigating, he spots the monster passing above him with Hyun-seo's arm hanging outside its mouth and gives chase, stopping Nam-joo from firing an arrow at it when it passes her. The two then chase the monster to the other side of the river, where a protest formed to lure the monster towards them for the army to dump a chemical known as Agent Yellow to kill the creature.

When the monster makes it to the shore and begins attacking the crowd, the army open up the container with Agent Yellow inside, covering the monster and the crowd. As the monster falls unconscious and the crowd flees, Gang-do pulls out Hyun-seo and Se-joo from the monster's mouth, only to be horrified to discover that Hyun-seo has been killed by the beast. Enraged, Gang-do attacks the creature when it awakens, but is quickly overpowered. Nam-il comes to his brother's aid by throwing molotov cocktails at it while the homeless man pours gasoline on it. Nam-joo sticks a flaming piece of cloth from one of the bottles on an arrow and fires it straight into the monster's eye, setting it ablaze. Before it is able to escape into the water, Gang-do impales it through the mouth with a metal pole, finally killing the monstrous mutant.

Trivia

 * The monster's inspiration, according to director Bong Joon-ho, came from a deformed fish with an S--shaped spinal cord caught in the Han River.
 * The original title of the film is Gwoemul, which is Korean for "Monster". It is unknown if Gwoemul is the name of the monster.
 * The monster, under the name Tadpole Thing, was ranked #10 on Cinemassacre's "Top 10 Giant Movie Monsters" list.
 * The monster was ranked #6 on Watchmojo's "Top 10 Lesser-Known Movie Monsters" list under the name Mutated Fish Creature.