Core-X

The Giant Core-X which uploaded the Varia Suit.

A Core-X is a type of X-Parasite typically found in creatures more powerful than those inhabited by weaker X. This X will remain intact even after Samus defeats its host due to a hard shell that can only be cracked with missiles. Once Samus breaks through the shell, she may absorb the X regaining one of her latent abilities in the process.

They will attack by ramming.

Hard Core-X

A Hard Core-X is an X in possession of a beam weapon that they may fire from an eye. Unlike regular Core-X, a Hard Core-X is only vulnerable when it is preparing fire its beam weapon and may only be damaged by a direct hit to its eye.