From publisher blurb:
One of the most prominent threats to the gods during their wars with the primordials was Orrori, the SunkenLady. Unlike most of the primordial, Orrori took a nurturing approach to her mortal worshippers, aiding them to build great cities of living coral in the Plane of Water. From these aquatic strongholds, they were able to extend their empire into the waters of other planes through a network of portals rivaling even the greatest ones found throughout the multiverse to this day.
Expanding upon Fifth Edition's rules, this PDF contains statistics for three aquatic foes, the Ikharri(first featured in Primordial Power), as well as Void Jellies and Coral Ghouls, monsters that can be found in an underwater Ikharri stronghold.