Kraken

The Kraken was a gigantic monster bred by Oceanus, the Titan of the Sea.

History
The Kraken was a child of Echidna, bred as a tremendous squid-like monster with immense physical strength enough to rock the oceans with its tentacles. At this point, the Kraken was described to be roughly half the size of the Atlantic Ocean itself during the First Titanomachy, and it was so terrifyingly powerful that Poseidon faltered and found himself and his subjects incapable of combating the monster on their own, and Zeus and Hades were too occupied with the other Titans and Kampe. Hades, when he saw the opportunity, prayed to Tartarus to produce a creature capable of combating the Kraken, and Tartarus unleashed an immense dragon called Kolasi.

The Kraken and Kolasi engaged in a spectacular battle that spanned for several hours before the dragon incinerated the inside of the sea monster and devoured its heart whole, killing it. It then proceeded to try to eat the Kraken, but it dissolved back into Tartarus. After the Titans lost the war to the Gods and Kronos destroyed, Oceanus's daughter Marion Marlin, an extremely powerful demititan, was chosen by Poseidon to be poetically imprisoned in a beast as dangerous and diligent as herself - he had the Kraken returned from Tartarus in a vastly smaller size, and imprisoned Marion inside the Kraken's belly, forcing her to remain inside the monster for all eternity.

However, after several centuries inside the beaast, Marion managed to penetrate the Kraken's powerful but simple mind and take control over it. She persuaded it to regurgitate her from its huge maw and then rode the Kraken back to Oceanus's palace, where it was kept as her pet. The Kraken was made use of by having it as an executioner for the entertainment of Oceanus's subjects - the Kraken would be fed prisoners and traitors and suchlike, and the residents of the palace would watch them be devoured by the giant beast.

Description
The Kraken was a squid of absolutely titanic size, it was theorized that it was roughly the size of the Pentagon. It has thick brown-grey skin that is described to be extremely thick, large golden eyes that gleam fiercely in the dark waters, and a tangle of hundreds of huge suckered tentacles that are devastatingly strong, able to rip ships apart with only one of them. Its mouth is described to be like the mouth of Charybdis, with a ring of serrated pearly-white teeth with a black pit for an inside. It has powerful lungs, able to suck in sharks and dolphins just by exhaling. Being inside the Kraken is described to be akin to being inside the worst sewer of all time, with thick muddy-red walls of skin surrounding and the constant sound of the Kraken's screaming. Its weak point is the heart, which is impenetrable from outside of the Kraken's body but from the inside it splits like wet paper if struck with Celestial Bronze or Amazonian Steel.