Amorphous. The Symbiote can move through a space as narrow as 1 inch wide without squeezing.

Spider Climb. The Symbiote can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Breathless. The Symbiote can't be suffocated.

Imitate Metal. It can take the shape of any metal object and it stays still, it is indistinguishable.

Immortal Creature. The Symbiote can only be killed if it's entire body is disintegrated. It can however be knocked unconscious.

Symbiotic Connection. The Symbiote can attach itself to a willing or unconscious creatures spine and leech of of its electrical charge, that it needs to survive. It will do everything to keep its host alive. It can however also violently leech the energy, which will eventually kill the host.

It can cover a tiny or large host with its body, giving it the same immunities and resistances that the Symbiote has. If the host takes thunder damage, the symbiote musst make a constitution check with the DC of 10+damage/2 or be disconnected from the host. Furthermore, it has its own turn while connected, so it attacks independently.

Compression. The Symbiote can compress its volume to take up less space and therefore change its size.

Magic Resistance. The Symbiote has advantage on checks against spells and other magical effects. 

Multiattack. The Symbiote makes five tentacle attacks.

Tentacle. Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing/slashing/bludgeoning damage.

Aggressive Leeching. If the Symbiote has attached itself to a creature, it can feed of of it and through that deal 28 (4d10+6) necrotic damage.