Your Strength increases by 2 and your Constitution increases by 1.

Symbiotes do not age due to their ability to regenerate.

Symbiotes are naturally Good, although depending on who they have bonded to their alignment can change. They usually take on a similar alignment to their host.

Symbiote’s bonded size varies wildly depending on what they are bonded to, Symbiotes are usually one size larger than their host. Without a host they are small.

Your speed is usually the host's speed + 10ft, while not bonded your movement is 10ft.

You bond to a host organism becoming one being, or at least an unwanted guest. You have a telepathic link with your host, being able to detect thoughts and emotional signals, although the host can choose to block out certain things if they wish and while bonded the host has advantage on checks made to mind control them.

 You can try to take control yourself without your host's command, if your host refuses you must both make a Wisdom Saving Throw, if you beat your host’s Wisdom Save then you activate the Living Suit ability. Every turn the host can attempt to regain control with another Wisdom Save, if the host succeeds then you will be forcefully retracted into the host. After a successful Overshadow you cannot attempt another until your next long rest.

As a reaction you are able to extend a pseudopod tentacle to prevent an incoming attack, roll a Dexterity Saving Throw against the attack’s roll. On a successful save, take half of the damage yourself. This ability only works on physical attacks, you are unable to block magic. You can do this a number of times equal to your Constitution Modifier + your character level. This can also be used to make an attack at a creature within 5ft, the attack deals 1d4 bludgeoning + 1d4 acid/poison/necrotic.

Symbiotes require a host to survive and though they can temporarily leave their host, they will need to return to them soon. A Symbiote can survive for 24 hours without a host, in this time they gain a point of exhaustion every 4 hours. They can temporarily bond with another host and drain them, doing so takes 1 hour and this removes all points of exhaustion and resets the time you can survive to 24 hours.

As an action and on your host’s command, you can cover your host with a living suit made of your own body. While transformed you are in control, can leap 3 times higher than normal, you and your host don't require oxygen and you act on your host’s turn. You can then retract as a bonus action. While transformed you gain the following features: 

Natural Armor. Your body is highly resistant to damage, your natural AC is 13 + Constitution Modifier.
Natural Weapon. At level 3 you are able to shapeshift your arms into one handed weapons, whatever weapon you use you are proficient in it and you do an extra 1d4 acid/poison/necrotic damage, this damage must be the same type as the Pseudopod ability. Level 8 the extra damage is increased to 2d4 and at level 10 the host can call upon this weapon while not being completely transformed.
Symbiotic Shards. At level 8 you are able to fire small hardened pieces of your body out at a target, the shards have a range of 40/80ft and do 1d8 piercing + your chosen damage type. At level 10 your host is able to fire the shards out without transforming, similar to Natural Weapon.
Devour. You can make a bite attack on a target that deals 1d6 piercing + your chosen damage type. If the bite kills the target you heal 1d8 + Constitution Modifier, any excess healing goes to your host. At level 8 the amount of healing is increased to 2d8 + Constitution Modifier, and the damage is increased to 2d6 + the chosen damage type.
Symbiotic Vulnerability. You are vulnerable to sonic and fire damage. When your Living Suit ability is active and you take either sonic or fire damage, you must make a Constitution Save DC 8 + base fire/sonic damage taken. On a failed save you retract back into your host for protection.

 You know any languages that your host knows and Abyssal.