X Parasite

The X Parasite (also known both singularly and collectively as "X") is an alien creature found in the Metroid Universe on planet SR388. It is not a true parasite as a parasite does not kill the host unless absolutely necessary. It is an ectoparasitoid. It kills the host and absorbs its DNA and intelligence. That ability means an X Parasite that absorbs several different species of animals both strong and intelligent would be able to dominate any sort of predator. Many X can come together and form one creature called a Core-X. The change is not chemical however and individual X can be forced from the Core-X.

Predators
The X have one predator, the Metroid. They were genetically engineered by the Chozo to destroy the X Parasites. After Samus Aran exterminated the Metroid race, the X population quickly multiplied. Despite their virulent nature they managed to hide their take over of the planet from the scientists in system until Samus Aran was attacked and infected by one.

Abilities
In addition to those previously mentioned abilities the X has several unusual abilities. Its ability to absorb intelligence also allows it to organically absorb and implement data, for example to create a heat resistant material to wrap itself in. It reproduces through a process similar to viruses, which makes it almost infinitely adaptable. When an X doesn’t come into contact with a susceptible host it stops growing and reproducing which means it needs no energy for food. It can float forever until disturbed. This makes it amazingly adaptable and incredibly hard to safely breed in laboratory conditions. They are also extremely and self-destructively aggressive, as they will even charge a foe it cannot hope to kill.