Three-Headed Shark

The Three-Headed Shark was a creature which appeared in the 2015 comedy-horror movie 3-Headed Shark Attack.

Description
As it's name might suggest, the Three-Headed Shark was a mutated Great White shark with three heads, a result of mutation caused by the heavily polluted waters of the Pacific Garbage Patch. It was far larger and more aggressive than a regular Great White, was attracted to pollution, and possessed an astonishing degree of regeneration, being capable of regrowing even the loss of a head.

History
After attacking the Persephone, an underwater environmental activisism and scientific research facility, the Three-Headed Shark managed to cause the station to explode, killing nearly everyone who worked there. However, a small group of survivors were able to make their way to the only surviving launch and make a getaway, although they were pursued by the hungry beast.

Unable to contact the Coast Guard, the survivors managed to radio a group of heavily-armed sports fishermen and request their aid, although it would take some time to arrive. In the meantime, the shark was distracted by a small ship full of teenage booze-cruisers, which it promptly attacked.

Realising that the vessel stood no chance against the shark, the survivors docked with the ship and managed to save a small number of the revellers before making their getaway on the Persephone's launch, once again pursued by the mutant.

At this point, the fishermen arrived, and while the shark killed two of their number, the third was able to chop off one of its heads, although he was killed shortly after. The party, having landed on a small island, met a single survivor of a previous attack who informed them that the predator was capable of emerging from the water for short periods to consume land-based creatures.

One of the scientists, realising that the shark was becoming more aggressive, deduced that this combined with its attraction to pollutants could be used against it, and the survivors subsequently managed to induce a feeding frenzy in the creature, driving its heads to attack one another and kill itself from massive trauma.