One ability score increases by 2 and another one by 1. Usually based on what you were dreampt up as; A dashing knight would be strength and charisma, powerful mage would be intelignence and wisdom.

Beholderborn mature and age at the same rate as the race that the beholder had drempt up. Usually human, maturing at the same rate as humans do and living up to 100 years, however if a beholder had drempt up a hero from a story they may have dreampt up that the hero is not just figuratively immortal (but not invulnerable) but actually lives forever.

Beholderborn are mostly the alignment associated with whatever their Beholder had dreampt into existance. A galliant knight is lawful good, a poweful mage is chaotic neutral. However your experience adventuring or serving may have changed your alignment to any other.

Being able to resemble any other race, you are medium or small.

Your base movement speed is 30 feet.

You can speak, read, and write Common, and Deep Speech. You also know one other language that your Beholder knew, and you determine if your beholder knew how to read and write this, or your character was created with this ability.

You are both an abberation and humanoid, and you are elligeable for feats and magic items that have racial restrictions.

Additionally, as a reaction you may reduce your falling speed to 60 feet per round (10 feet per second) for 1 minute, and if you land before this ends you take no falling damage and can land on your feet. You can use this a number of times equal to your proficiency modifier, per long rest

From your beholder origins, you have the ability to shoot out an eye beam from your eye(s) in a 25 foot cone in the direction your eye(s) are facing. Choose which beam to create, or roll on the table. When you take the attack action, you may replace one of your attacks with these beams and the charge of that beam is extended, and you may instead choose to use one beam without extended a charge and use it for free, and gain a point of exhaustion. Your DM may at any point force you to use this feature, and if so, you do not gain a point of exhaustion and they choose the beam. Your eyebeams count as magic for the uses of antimagic, but not for other purposes such as barbarian rage.

You gain 2 charges of each beam at 5th level, and 3 at 11th level.

Your modifier is constitution, or intelligence, wisdom, or charisma, saving throws are 8+proficiency bonus+modifier.

 (Pink) Charm or fear ray- each creature must succeed a wisdom saving throw or be charmed or frightened by you for a number of rounds equal to your proficiency bonus, and at the end of their turn they can repeat the saving throw.

(yellow) paralyzing ray- each creature must succeed on a constitution saving throw or be paralyzed for a number of rounds equal to your proficiency bonus, and at the end of their turn they can repeat the saving throw. 

(grey) slowing ray- each creature must succeed on a dexterity saving throw or the target’s speed is halved for 1 minute. In addition, the creature can’t take reactions, and it can take either an action or a bonus action on its turn, not both, and at the end of their turn they can repeat the saving throw. 

At 5th level, you can use:

(orange) disintegration ray- each creature must succeed on a constitution saving throw, or take a number of d8's equal to your proficiency bonus as force damage (half as much on a success), and portions of what the target is wearing or wielding are disintegrated into fine dust.

(blue) Antimagic beam- you create a cone of antimagic, as in the antimagic field spell, however if the creature succeeds on a saving throw of their casting ability modifier against your saving throw dc, the spell goes through regardless. This lasts a number of rounds equal to your proficiency bonus. and ends at the start of your turn in that round, and always faces the way your eye(s) are facing.

Additionally, you may use your eye(s) as a spellcasting focus.

Beholderborn are of the names relevant to the race dreampt by the Beholder that said Beholder knows, or assumes, however you may also choose your name for yourself based on what other Beholderborn called you during service or what you decided to name yourself during your adventures.

Your abberant biology gives you some benifits: you have proficiency in perception, advantage against being charmed or frightened, and you can communicate telepathically to any creature within 30 feet. You have a racial trait from the race you are based on and you may also roll for or choose a random mutation from the table below:

Your eyes bulge from your skull. You can see normally in darkness and dim light for 60 feet, but you have disadvantage on performance and persuasion checks.

Your skin is scaly and hard. While not wearing armor, your AC equals 13 + your Dexterity modifier, but you have disadvantage on dexterity saving throws.

Your eyes glow with bright unnatural light. You can see magic as if under the effects of the spell detect magic, but you have disadvantage on stealth checks.

Your skin excretes a sticky viscous liquids. You have advantage on all Athletics checks to made to climb and to grapple, but disadvantage on escaping being grappled.

Your hands and feet have webbing between their fingers and toes, and your skin is shiny and slick. You gain a swim speed equal to your walking speed, and you can breathe air and water, but have disadvantage on being poisoned and saving throws against poison.

You have an extra arm or two sprouting from your body. You cannot use this arm to wield weapons or use shields, but it otherwise functions as normal. In addition, you can take the use an object action as a bonus action, allowing you to use items that normally requires an action to use, such as a potion of healing or bag of ball bearings, as a bonus action, but you have disadvantage on insight checks.

In addition to these, you may choose any bodily abnormality that you wish, talk with your dm to weave this into conversations and encounters, and how others judge you for these.