Metroid Database Bestiary

A large bioform created when X gather in large numbers. Masses of X are required to infect larger creatures, and once their host body is destroyed, the Core-X is revealed. The Core-X is a gelatinous blob protected by a reinforced spiked cellular wall that can only be damaged by missiles; shooting the core with beams will only reflect off and release small X parasites that form the wall. If the Core-X is struck by a missile, it will release large amounts of electrical energy to protect its cell wall from further attacks. However, doing so expends large amounts of energy, so cannot be sustained for long periods. Core-X are incredibly dangerous, but are relatively weak compared with their host bodies.

Appears from the remains of a defeated boss. The Core-X will attempt to ram Samus, but can be easily dodged by jumping over it or hitting it with a missile. The Core-X can only be damaged with missiles, and after the Core-X is hit, it will be invincible for three seconds. Core-X will take 3 to 8 missile strikes before they are defeated, depending on the boss. If you shoot the Core-X with your beams, small X will fly out of it; collect these X to refill your energy and missiles. Once defeated, collect the Core-X to gain full energy and missiles, as well as a new power-up.