You can speak, read and write Common, Deep Speech and one other language of you choosing, at the DM's discretion. 

You are an Aberration.

You are Tiny. 

You have a walking speed of 30ft, and a swimming speed of 40ft.

When you are in your true form, You can squeeze through a space as narrow as 1 inch wide, provided you are wearing and carrying nothing. You have advantage on ability checks you make to initiate or escape a grapple.

you can create a Disguise, a specialised organic suit designed to appear as and perfectly mimic other life. the Disguise is neurally linked to you when you enter it, meaning you see through it's eyes, eat and breathe through it's mouth, and feel through it's hands as if it were your own real body.

When you enter a Disguise, you gain all of the Disguises racial traits, overwriting your physical traits such as Speed, Size and Creature Type (note that for your Creature Type, the Type you gain is added on to your current one, not replaced. for example, if you use the Disguise of an Elf, you are considered both a Humanoid AND an Aberration.)

When you select this Race, you can choose an additional Race to be already Disguised as, or choose to stay in your true form.

A Disguise can be created or changes to suit another Race during every Long or Short Rest, or in general as a Action for one hour. If you are interrupted during this, the Disguise falls apart and is rendered useless, requiring you to try again. 
to be able to create or change a Disguise to a certain Race, you need to have consumed a certain amount of genetic material from that Race (e.g tissue, bodily fluids, etc.).
Regular Races (Human, Dwarf, Elf, Gnome, Aaracocra, Goliath, Giff, etc.) 1 cubic inch
Half-Breeds and Planetouched (e.g Half Elf, Tiefling, Genasi, Half Orc, etc.) 5 cubic inches
Semi-organic/Non-humanoids (e.g Plasmoid, Warforged, Thri-Kreen, etc.) 10 cubic inches

When making a Disguise, it will initially look like a mix of all the genetic data used to make it (unless there is only one donor, in which case it will be identical to them), but you can, as an action, warp around the Disguise's face and features to suit your desires. 

As a Bonus action, you can also choose to exit your Disguise and move up to half your movement speed.

When your health drops to 0 in a Disguise, you instead move 5 ft in the opposite direction, doffing the Disguise in your true form with half your Hit Points minus any additional damage that was left over. if the damage that did this was Psychic damage, you do not exit your Disguise and fall to 0 Hit Points anyway.

Devolving away Psychic powers from your Beholderkin brethren has left parts of your brain walled off and weak to Psychic influence.

You are vulnerable nerable to Psychic damage, and all forms of telepathic communication expose you as a Watchling.

If you gain a form of telepathic communication yourself, such as through Aberrant Mind Sorcery or a pact with a Great Old One, the psychic damage vulnerability is removed, as you unlock the psychic powers your kind once had before you.