Nidor, a world given life by titans
Roaming the ocean, an elderly Nightwave (a grand creature from a horrific race of undead) stalks for prey in the form of ships and small fleets. A colossal shark like creature of shadow/negative energy, this elderly nightwave lets loose a wail (similar to that of a banshee) to snuff the life of all but the hardiest of adventurers. From there, it slowly encircles the survivors, letting the black water it taints around it freeze the bottoms of the remaining ships. As the vessel begins to sink, the nightwave slowly opens his maw, lazily swimming in, gulping down the victims and evaporating what remains of anything living onboard.
Because no one has survived a direct attack by this creature, it is unknown if other undead swim or follow it in any capacity. The largest group of people to have survived an attack by the nightwave are known as the Western Refugees, a fleet of vessels that fled from Yccona to escape the battles between Lamashtu and the eyes of fear and flame.