You are vulnerable to cold damage.
Additionally, you have disadvantage on saving throws due to cold weather or conditions.

Any creature or object grappled by you must succeed a constitution save (DC 8+Prof.+CON modifier). Or take acid damage (1d4 x Half character level rounded up).
Objects damaged this way can be destroyed (10hp per size category above tiny).

Any time you would be in contact to more than one gallon of water you take 1d6 necrotic damage for each round you remain exposed to it.
You cannot be reduced to zero Hp in this way, minimum Hp is equal to your CON modifier.

Your alien body provides a number of unique traits.
You are immune to the prone condition.
You can feed on any organic material.
You do not need to breath.
You can pass through openings 1/4 the size of your normal form.

While you may wear clothes and items, you cannot benefit from wearing armor

Your Constitution score increases by 4, and your Dexterity score increases by 2, all other scores are reduced by 2.

Formless, much like their wild relatives, seem to live for as long as they have plenty of food to eat. However, the longer they live the more sustenance they require causing the average age to be around 500 years. 

Formless are often neutral, seeking only to prolong their own life and feed, caring for little else. But, some have been known to take influence from others and portray the same range of emotions and moral obligation. 

Formless change in size and mass over time, but are typically are around 200lb 5ft in diameter, or roughly the same size and shape as most humanoids. Your size is small or medium.

Your base walking and climb speed is 20 feet.

You are immune to Acid damage and the poisoned condition.

Additionally, you are resistant to slashing, piercing, and bludgeoning damage.

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