Monster Codex: The Sea Serpent
Sea serpents are a sailor's worst nightmare. These reptilian monstrosities are highly territorial, and will attack anything that enters their feeding grounds. It is recommended to avoid sailing over a sea serpent at all costs. You will not survive.
Sea serpents are some of the largest predatory animals in the world, although no actual measurements have been made due to their aggressive and elusive nature.
There are reports that harpoons are unable to penetrate the scales of a sea serpent. This is true, and is yet another reason not to seek out these underwater terrors.
