Your Dexterity and Intelligence scores increase by 2, but your constitution decreases by 1

Reaching maturity at around 20 years, their incredibly long, if not indefinite lifespans surpass that of the elves, at around 1000+ years. It is unknown as to whether or not this is the limit to their age, however, as it is uncommon to see a dark young let alone one who has survived for that long

Thanks to your writhing, octopus-like appendages, you not only gain a climbing and swimming speed of 20, but also gain the ability to move over rough terrain as if it were normal terrain, and to climb across any wall or ceiling. You also gain advantage on grappling saving throws. These effects are only active in the absence of medium or heavy armor, and no weapon attacks may be made while on a smooth wall or ceiling.

Lacking a mouth, the dark young have evolved limited telepathic capabilities that allow them to project their voice into the minds of those they wish to speak to. This effect maxes out at 5 people, and attempting to project upon any more results in 1 psychic damage upon failure of a DC 10 intelligence saving throw.

Not unlike a beholder, your cosmic heritage allows you to manifest a beam of pure energy from your eye. A creature takes 2d6 lightning damage on a failed save, and half as much damage on a successful one. The damage increases to 3d6 at 6th level, 4d6 at 11th level, and 5d6 at 16th level. After you use your eye laser, you can’t use it again until you complete a short or long rest. This ability can also be used as a harmless laser-pointer, or flashlight whenever desired.

A lack of substantial body structure leaves you vulnerable to cold damage.
Your dark heritage leaves you vulnerable to radiant damage.
when hit with these damage types, you take double damage of that type.

Your cosmic heritage, hailing from an outer god of the eldritch pantheon, removes the need to eat or breath.

You can speak, read, and write Common and Deep Speech. Deep Speech was the language of aberrations, an alien form of communication originating in the Far Realm.

About the same size as the average human, the dark young generally stand around 4 to 5 feet tall, and usually have a weight to match. Your size is medium.

While not being able to completely change it's body structure, the dark young do exhibit the ability to create appendages and orifices over the span of a short or long rest, depending on the complexity. It should be noted that any orifices created need to first be opened manually and maintained every day, lest they close up again.