Leviathan

The Leviathan is an aquatic and hostile creature found in Shoreline. It is the largest creature in Rain World, sometimes caught killing even vultures (which is a good thing). On closer look and with some luck that its head comes to the surface (which rarely happens), you can actually see that it is a carnivorous plant/biomass having infested a mechanical construction.

The leviathan is the only non-static creature that physically eats things, instead of bringing it to a pipe.

Trivia (Contains spoilers!)

 * The leviathan or sea creature shares the model shape with the Void Worm.
 * It can eat anything besides its own kind.
 * Its tail sometimes whips at the garbage formations but isn't dangerous.
 * In extremely rare cases, albino leviathans can spawn. However, these do not spawn in sandbox mode.
 * A design similar to the leviathan is mentioned in a miscellaneous pearl as a schematic for refuse reclamation automaton, suggesting that the mechanical component of the leviathan was part of a waste recycling machine.