The X Parasites are the main antagonists in the video game Metroid Fusion. They are hostile parasites that were the Metroid's prey, but after the Metroids became near extinct, the X Parasites took over a space station where Metroids were being researched, and caused enough threats to nearly wipe out the universe if it wasn't for Samus Aran.

They have the ability to take the form of anything they make contact with. Doing so, the X Parasites created SA-X, B.O.X., Nightmare, and Neo-Ridley, and so much more.

They're also the Bigger Bads of the entire Metroid series, as their existence is the reason that Chozo created the titular creatures in the first place.


The appearance of an X Parasite is that of a floating gelatinous life form. The structure of their bodies allow them to slip through the pores of an organism or crevice if any surface. They have the ability to multiply via asexual reproduction.


Yellow X

The most basic and common type of X Parasite. When absorbed, they restore ten units of energy. A single Yellow X was responsible for infecting Samus and nearly killed her if it wasn't for the Metroid vaccine.

Green X

Green X appear after Samus regains her Missile Launcher. Similar to Yellow X, the Green X can be found anywhere on the BSL station and excrete from most enemies. They restore two Missiles when absorbed.

Red X

The rarest out of the three common X Parasites. Normally appearing from Gadora-X and other strong enemies, they restore 500 units of Energy, 10 units of Power Bomb Ammo, and 50 units of Missile Ammo upon absorption.

Blue X

The Blue X (or Cold X in Japanese) are a special type of X Parasite that have adapted themselves to the cold temperature of Sector 5 of the BSL station. Apparently, the X Parasites deliberately forced their evolution to stop Samus from exploring the rest of the space station, explaining why Blue X have invaded Sector 6 as well. Until Samus obtains the Varia Suit, Blue X will chase down after Samus and, due to the Metroid vaccine, absorb themselves into her in order to damage her, although Samus can shoot at them to temporarily stun them. After Samus regains her Varia Suit, Blue X will rather flee from Samus instead. Blue X will both inflict and restore 30 units of energy. Because of their added cold immunity, they are much larger than regular X Parasite and are oddly unable to infect and possess a host due to their size or cold body temperature.




Core-X are the largest and strongest members of the X Parasites. They have incorporated themselves into either an important ability from the DNA of their victims or one of Samus's lost power-ups. They take the form of a boss and, upon defeat, reveal their natural form. The Core-X were originally regular X Parasites, but the source of their prey made them stronger and allowed them to produce X Parasites at an alarming rate.

First Variant

These Core-X are protected by a strong outside shell that have to be broken with Missiles until their nucleus can be obtainable.

  • Arachnus: Morph Ball
  • Zazabi: High Jump Boots and Jumpball
  • Serris: Speed Booster
  • Mega Core-X: Varia Suit
  • Yakuza: Space Jump
  • Nightmare: Gravity Suit
  • Neo-Ridley: Screw Attack

Second Variant

These Core-X hold a power-up beam that can only be damaged when they expose their nucleus-like eye from underneath their Missile immune exterior. Their eyes only open when they are about to shoot out a laser, so Samus should be cautious on timing her shots.

  • Fake Chozo Statue/Elephant Bird: Charge Beam
  • Scientist: Wide Beam
  • Nettori: Plasma Beam
  • B.O.X.: Wave Beam
  • SA-X: Ice Beam and Unnamed Suit


           Metroid Villains

Space Pirates
Mother Brain | Ridley | Kraid | Phantoon | Draygon | Omega Pirate | Ridley Robot

Queen Metroid | Metroid Prime | Dark Samus | Alpha Metroid | Gamma Metroid | Omega Metroid | Zeta Metroid

Emperor Ing | Amorbis | Chykka | Guardians | Quadraxis

X Parasites
SA-X | Nightmare | B.O.X. | Neo Ridley | Nettori

Galactic Federation
The Deleter

Diggernaut | Ruins Test

Sylux | Sheegoth | MB | Crocomire | Gorea | Phaaze | King Worm | Parasite Queen | Vorash