Poisons

Poisons are a race of crystalline extraterrestrials featured in Marvel Comics. They are very weak in their base form, but can assimilate Symbiotes to become much more powerful creatures.

When they assimilate a symbiote (which is usually done after impersonating a target's loved ones or by ambushing them), the Poisons gain the powers, abilities, memories, and personality traits of the host, who is consumed for nutrients to fuel the bonding process.

HIStory
The Poisons were prey to larger, stronger creatures for an unknown amount of time. Then, they were discovered by an incarnation of Stephen Strange bonded with the Venom symbiote and discovered that they could assimilate Klyntar to become more powerful. Strange then formed a Resistance of Venomized heroes and villains, but most of them were either killed or joined the Poisons' ranks.

The Poisons, led by one who consumed Doctor Doom, planned to consume Strange and use him to summon all the Venoms they could assimilate, mostly unaware of stronger symbiotes like Carnage, an incarnation of whom was summoned to aid the Resistance as a secret weapon. Several Poisons were killed when the Resistance, aided by a Poisoned (but still himself) Deadpool, infiltrated their ship to rescue Strange and set it to self-destruct. Doom escaped and reported to the true leader of the Hive, Poison Thanos, who became aware of the Multiverse and sought to conquer it.

The Poisons managed to travel to the Prime Marvel Universe, hiring a symbiote poacher to raid the planet of Klyntar, killing the Agents of the Cosmos and abducting every symbiote from the planet. They then altered the symbiotes to make them more susceptible to assimilation and proceeded to bond them with every superhero on Earth. "Anomalies," such as the mainstream Cletus Kasady, Kid Kaiju, and Agent Anti-Venom were to be either assimilated or killed to assist in their conquest.