Leviathan

Leviathans are the largest creatures of the sea, bigger and heavier even than the giant kraken. They live in warm seas worldwide but are seldom met. They measure 200-300 feet; reports of animals near 400 feet are usually put down to exaggeration. A leviathan looks like a colossal tortoise with a dragon's head, webbed claws and a crocodile's tail. Coral, shellfish and seaweed grow thickly on its shell, so sailors sometimes mistake a basking one for a small island or reef, usually with disastrous results.

Territorial but not aggressive, they pose little danger to people. They eat mostly plants, only occasionally adding fish and small crustaceans, and almost never attack ships or large animals unless provoked; most sinkings blamed on them are thought to be accidents. Their only known foes are kraken, which they attack on sight, and sea dragons, which they drive out of their waters. Sailors call a battle between leviathan and kraken the most terrifying sight at sea, and such fights are said to stir up whirlpools and tidal waves.

Because they keep kraken and sea dragons away, some primitive island tribes worship leviathans as demi-gods, offering them heaps of herbs, fruit and crustaceans and taking revenge on anyone who harms one. Angered, a leviathan is fearsome: its talons split a hull like an eggshell and its jaws can swallow a horse whole, which it manages on a d20 roll of 19 or 20. Its shell, up to three feet thick, is nearly impossible to damage from above or below, though the head, neck and limbs have only leather-tough hide. If pressed hard it pulls into its shell and sinks beneath the waves.