Stick to the low ground and fire charged beam shots directly at the SA-X to destroy it. Your beam must be fully charged to damage it. As it approaches, Space Jump over the SA-X to the other side of the floor while charging your beam, and release the shot when you land.

Chronologically speaking, SA-X is the second doppelgänger/clone of Samus Aran, with the first being Dark Samus.

Metroid Fusion is overtly a horror game, trapping Samus in a claustrophobic research station where all life (including other humans) has been eradicated and replaced by parasites capable of exaggerating their shapeshifting forms.

We all know they had to surgically remove most of Samus's suit from her but that pieces of it were stuck to her body and couldn't be taken without killing her.