Fingerlings were generally not treated as individuals until they'd survived to physical maturity. Kuo-toa lived to be approximately sixty years old.

Kuo-toa were normally 5 feet (1.5 meters) tall and weighed approximately 160 pounds (73 kilograms). Your size is medium.

Accustomed to life away from the sun's blinding light, you have superior vision in dark and dim conditions. You can see in dim light within 120 feet of you as if it were bright light, and in darkness as if it were dim light. You can't discern color in darkness, only shades of gray.

You have disadvantage on attack rolls and on Wisdom (Perception) checks that rely on sight when you, the target of your attack, or whatever you are trying to perceive is in direct sunlight.

You can speak, read, and write Common, and Undercommon.

The kuo-toa can breathe air and water.

The Kuo-Toas have been irrevocably altered by the torment they suffered at the hands of the Illithids, and their unique connection to madness and eldritch forces allow them an otherworldly perception. The Kuo-Toa can sense the presence of any creature within 10 feet of it that is invisible or on the Ethereal Plane. It can pinpoint the location of such a creature that is moving.

The skin of a Kuo-Toa is coated in a thin layer of mucus, allowing them to more easily wriggle their way out of tight situations. The Kuo-Toa has advantage on ability checks and saving throws made to escape a grapple.

Your Constitution, Intelligence, and Wisdom scores each increases by 1.

Your base walking speed is 30 feet. Kuo-Toa are naturally adapted to move unhindered underwater, you have a swimming speed of 30 feet.

Kuo-toa were extremely suspicious as well as duplicitous, betraying trust for their own benefit so long as they believed they could do it successfully. To a Kuo-toa, survival and worship is very important, the dual concerns of any Kuo-toa amongst others of its kind. Typically this resulted in most Kuo-toa adopting a neutral evil alignment. The mental oppression they suffered at the hands of other races broke the already-simple minds of most kuo-toa and as a result madness was a common ailment amongst their kind. Kuo-toa were not all necessarily evil, but within their repressive theocracy, common kuo-toa did not possess anywhere near enough willpower to oppose the ruling castes. When separated from these societies, kuo-toa could adopt neutral or good philosophies such as pacifism

The madness of your broken mind is infectious, like a virulent disease. You're mildly telepathic, but any creature your mind comes into contact with experiences the madness afflicting you, which threatens to drive them insane. It's worse than useless for any attempt at communication, and strains your mind intensely, but you have learned to harness it to the detriment of those who you wish harm.

Once per long rest as an action you can attempt to drive a creature within 30 feet of you insane, they must succeed on an intelligence saving throw or have disadvantage on attack rolls for one minute. A creature that's immune to being frightened or a creature with an intelligence score lower than 3 automatically succeeds. An affected creature can repeat this saving throw at the end of each of their turns, ending the effect on themselves on a success. The DC is equal to 8 + your proficiency bonus + your intelligence modifier.

In addition, if a creature fails the initial save against this effect by ten or more, they're afflicted by a randomly determined short term madness from the short term madness table (DMG). This effect also ends on them if they pass the saving throw described above at the end of their turn.