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.