X Parasite

The X Parasite is a parasite witnessed only in Metroid Fusion. Mysterious, intelligent, and self-propogating organisms, the X were first encountered on SR-388 as Samus Aran watched over a Biologic's Research team when the X parasite came out of the carcass of a dead Hornoad. The X infested Samus's central nervous system and rendered her unconcscious. Shortly after, Samus had to have various important parts of her Power Suit removed, some of them even surgically. After being infected, the X could not be removed from Samus's central nervous system, and she was given a very small chance of survival. Then, in a turn of luck, the Galactic Federation found a cell culture from the last infant Metroid and quickly injected it into Samus. Luckily, the X were completely and quickly destroyed by the infant Metroid's cells. Samus then gained the ability to absorb the X into her system. However, at the end of this adventure, Samus crashed Biological Space Laboratories into SR-388 before evacuating, destroying both and presumably wiping out the X.

X are capable of infesting other organisms and mimicing their prey. One notable example is the SA-X: X parasites found their way to Samus's old suit. At least ten SA-X with extreme destructive power were present on BSL.

Yellow X
Yellow X are the basic types of X. They restore 10 energy. Yellow X come out of most normal enemies. The Yellow X first appeared in the cutscene at the beginning of the game, where it had infected a Hornoad.

Green X
Green X will appear when Samus gets the Missile upgrade. These restore 3 Missiles and 1 Power Bomb.

Red X
Red X emerge from Boss Doors and a select few other enemies. They restore much health and all Missiles and Power Bombs. They are very rare.

Blue X
Blue X can only be absorbed once Samus obtains the Varia Suit due to their ability to freeze from within. They restore 30 Health. Otherwise, they cause considerable damage to Samus, who is highly sensitive to cold, thanks to the Metroid vaccine. They are often found in groups.

Core-X
Once a boss is defeated, it will turn into a Core-X. The Core-X is surrounded by a tough shell, and to break, you need to hit the shell with a missile. If the shell is flashing, then it will not hurt the Core-X. Once you hit one, it will spit out Yellow and Green X to replenish your stamina and weapons.

Hard Core-X
More difficult to defeat than normal Core-X, Hard Core-X come out of bosses that will give you a beam ability. To damage them, hit them when their eye is pointed toward you. Once you have done that, they will fire their respective beam at you, so watch out! The Hard Core-X bosses in Metroid Fusion are:
 * Fake Chozo Statue (Charge Beam)
 * Scientist (Wide Beam)
 * Nettori (Plasma Beam)
 * Security Robot BOX (Wave Beam)
 * SA-X (Ice Beam)