Nightmare

Nightmare is the eighth boss Samus faces aboard the Biologic Space Laboratories research station in Metroid Fusion.

Biography
Nightmare is "a bio-mechanical organism designed for military applications" and "possesses uncommon power and can manipulate gravity". Once Samus is leaving Sector 5 for the first time, she sees him behind a large glass flying around. Later on, Adam detects an explosion in Sector 5 and tells Samus to investigate. Samus goes to the sector and eventually finds Nightmare, a ghastly bio-droid.It is interesting to note that the Nightmare appears damaged. This is probably due to its rampage around the sector, but it adds to the Nightmare-ish appearance, making him look decomposed and rotting.

The battle
This battle has 3 phases, not including its Core-X form.

Phase 1
During this phase, Nightmare will stay in front of Samus, and shoot bursts of lasers at regular intervals. These bursts are sometimes hard to jump over, since he shoots them in a spread. He attempts to slowly follow Samus's movements.

His weak point is his Gravity Manipulator - the glowing purple protrusion from his central body. Normally, his arms will be blocking it, so Samus must lure him up by jumping high, then coming down and getting a shot or two at it using a charged Plasma Beam shot or an Ice Missile, then running back. Once he has been sufficiently damaged, he changes to Phase 2.

Phase 2
Now, his Gravity Manipulator will start running, and the room will start to warp. His mask's eye holes will start to ooze slime at this time. Samus's jumps become harder to control due to the gravity manipulation.

Ice Missiles are now useless, falling to the ground when shot. After some more damage, the Gravity Manipulator is destroyed, returning gravity to normal, and his face mask will be blown off, revealing his true face.

Phase 3
Nightmare begins moving erratically around the room, becoming extremely difficult to dodge. His exposed face is now his weak point. Samus must utilize the ladder and the Space Jump to avoid his attacks and to aim counterattacks effectively.

When he and his Core-X are defeated, Samus's Gravity Suit is restored.

Trivia

 * There is an enemy in the Nintendo DS game, Mario & Luigi: Partners in Time called a "Snoozorb." It shares similarities in body plan, face, and name (pertaining to sleeping). Snoozorbs attack by either shooting a laser beam or changing into a ball shape and rolling into the Bros.