Kuo-Toa

Their language shares roots with Undercommon, the main language of Tritons.
Writing is likely limited culturally to the "Elders" and shares an alphabet with Undercommon, though even non-elders seems capable of reading.
There are at least two phenotypes: piraña green, lower-caste, and purple, higher ranking.
Some leaders at least can carry horned staves and teeth strung into necklaces, as well as call upon divine energies.
Kuo Toa don't worship gods, but they create them out of amalgamations of refuse. This is possibly enough for their faith to bridle magic.
Kuo Toa's eggs need water, but their nests can be in amphibious settings (like coastal caves with brine pools)