The Leviathan

The Leviathan is the boss of the Cursed Waters. "The beast of legends, The Leviathan has revealed itself within the Cursed Waters, lurking in a boney graveyard. Not only is this a fearsome beast with its hull-shattering beak and claws, but she's clever too, known to dash away only to ambush its prey from new angles."

- Version 0.9.0 Update Notes

Description
The Leviathan is a legendary beast that lurks within the wretched domains of the Cursed Waters. An enormous being divided in many enormous, jagged segments and using its two ferocious claws to dilacerate whatever stands in its way, this behemoth is not to be underestimated. Many have fallen victim to the piercing bite of the giant's bloodied beak, and the few who have survived its maleficent grasp spread tales of the creature's brutality and superior acumen. Its origin, like much of the paranormal environment it lives in, is unknown to mankind, but one thing is for certain: Any who defy the Cursed Waters and invade upon the Leviathan's realm will eventually fall victim to its unparalleled ferocity.

Behavior
The Leviathan has multiple ways of attacking the Submarine: It is capable of using its powerful beak to pierce the vessel's hull, using its powerful claws to rend anything below and, perhaps most menacingly, it is capable of using the arena to its advantage, by dashing across the screen to prepare a charge from the background and into the submarine, during which time it cannot be hit.

Trivia

 * The Leviathan is a sea monster from the jewish religion. We Need to Go Deeper's Leviathan, however, may also be based on H. P. Lovecraft's Leviathan, a child of Cthulhu.