Fist of Drakkengarde
The Fist of Drakkengarde was a massive galleon in the Mercantile Alliance's navy, used to patrol the Dragon Sea to defend merchant vessels against pirates. The largest and most heavily-armed ship in the fleet, it was long considered unsinkable... Until it went down with almost all hands lost. Only one survivor was ever found, half-mad and clinging to a piece of driftwood.
According to his story, one night every member of the crew suffered the same horrific nightmare of the complete destruction of the ship, the crew either drowning or being devoured by a terrifying sea monster. They awoke to find the ship overrun with kuo-toa and men with slimy, translucent skin. This horrific army slaughtered the crew and destroyed the ship, of which no trace beyond the sole survivor was ever found. Divination magic revealed naught but a name: Yngukulub the Devourer.