Deep scion

Deep scions are humanoids who surrendered their bodies and souls to an aquatic power in exchange for their lives, and became amphibious shapeshifters in the service of the higher power.

Description
Deep scions are amphibious creatures with dark tendrils that pull off of its headwith and toothy fangs covered by two flaps of skin. Their skin has a bluer or bluish-green tint to it, their hands are elongated, and eyes are yellowish-green in color and sunken.

Abilities
The deep scions can use its action to polymorph into a humanoid-piscine hybrid form, or back into its original form. Its statistics, other than its speed, are the same in each form. Any equipment it is wearing or carrying isn't transformed. The deep scion reverts to its original form if it dies.

In their hybrid form, deep scions are able to make an audible a psychic screech within 300 feet that recharges after a short or long rest. Creatures within 30 feet of the deep scion must succeed on a Wisdom saving throw (DC 13) or be stunned until the end of the deep scion's next turn. In water, the psychic screech also telepathically transmits the deep scion's memories of the last 24 hours to its master, regardless of distance, so long as it and its master are in the same body of water.

Known deep scions
All deep scions who attacked the Mighty Nein during their adventures were in the service of Uk'otoa:
 * One deep scion defended the second seal of Uk'toa.
 * Three deep scions attacked the Balleater in, apparently seeking the Cloven Crystal still within Fjord, and succeeded in killing him although not in recovering the crystal.
 * Another deep scion, supporting undead Avantika and three chuuls to seek out the crystal, attacked the Mighty Nein aboard the Midnight Hammer in the Frigid Depths.
 * Seven deep scions attacked the Nein Heroez with Fjord, Jester, and Kingsley aboard, successfully retrieving the last Cloven Crystal.