Leviathan
Leviathans are horrific creatures of such sheer size as to defy all mortal perception. The mind only processes fragments: a vast blackness that blots out the sea, howling winds that follow the rippling of its oily outer membrane, a submerged presence that sucks the air from the lungs of any unfortunate enough to be near. The mindless, formless heaving and thrashing of these beasts can craft tidal waves and whip air into a hurricane-like frenzy of destruction.
Leviathans are often sighted far beyond land, on the Phocian Reaches. However, one such hideous beast actually lives in a cave near Mhaldor on Sartan's Island. It was originally summoned in the year 339 AF by Mhaldorian ritualists and then slain, its corpse used to bridge the gap over Gruu'n Chasm.
As terrifying as its oceanic brethren, this monster is so immense that it is impossible to focus on its features completely. It is notorious for killing newbies who become lost on their way to Mhaldor, and its cave is often littered with odds and ends dropped by these poor souls.