Nightmare

Nightmare (ナイトメア) is described as a "a Bio-Mechanical organism designed for military applications that possesses uncommon power and can manipulate gravity". Nightmare appears as a boss in both Metroid: Other M and Metroid Fusion, in which Samus has to defeat the creature while enduring its gravity manipulation abilities.

Biography
Chronologically, Samus first encountered Nightmare in Metroid: Other M while on her journey to Sector Zero on the Bottle Ship. The creature fights Samus twice; once when she tries to enter Sector Zero, and again when she tries to exit Sector Zero. When first defeated, Nightmare's face will tear off while colliding with the walls due to the malfunctioning of its Gravity Manipulator, until the beast finally crashes to the ground. When Samus returns to the area, Nightmare will struggle to get up while making screeching noises, and the duo do battle once more. After the second battle, Nightmare will explode into pieces, leaving only the head intact with the rest of its body parts scattered. Its corpse rests on the ground until the post-credits sequence: the Galactic Federation seemingly salvages the remains of the creature during their thorough investigation of the Bottle Ship and transports the body at an undetermined time to the Biologic Space Laboratories research station.

In Metroid Fusion, Samus first encounters Nightmare in the X-Parasite infested BSL station when leaving Sector 5 for the first time, where she catches glimpses of Nightmare's silhouette flying around behind large windows (possibly part of its containment tank), causing the entire room to shake violently. It also appears when she is entering and leaving Sector 5 while obtaining the Power Bombs, though it is never mentioned by Adam after any of these encounters. After Samus obtains the Plasma Beam, Adam detects an explosion in Sector 5 and tells her to investigate. As she arrives at the entrance to the sector, Adam finally informs her of Nightmare's continued existence. Samus finds most of the arctic sector in ruins and by exploring further, she eventually finds the X-infected Nightmare in a room that seems to be entirely filled with mechanical junk. It is interesting to note that the organic part of Nightmare's face appears to be deteriorated; the cause is unknown, but the decay makes the creature all the more frightening once its mask is destroyed.

Nightmare


Nightmare floats in the middle of its room, firing energy blasts at Samus. It will sometimes spin in one place, firing lasers, and may even try to ram Samus. Nightmare will manipulate the gravity and slow Samus down, allowing it to attack her more easily. To disable Nightmare's Gravity Manipulator, Samus must shoot repeated Beam shots at it. Interestingly, the Gravity Manipulator pulls her shots towards it, even though in Fusion, beam shots are unaffected by gravity manipulation. Eventually, Samus will freeze its Gravity Manipulator, causing it to momentarily shut down. Samus is able to utilize this period of normal gravity to fire at Nightmare's face with Super Missiles or Missile Launcher (its faceplate reflects Beam shots), otherwise the Missiles would collide with the ground. This will destroy the faceplate and Nightmare's gravity powers will go out of control, causing it to slam into the walls of the room twice before falling to the floor. Believing Nightmare to be dead, Samus ventures off to Sector Zero.

Nightmare Unmasked


As Samus leaves the area after inspecting Sector Zero, Nightmare's body suddenly rises up and attacks her in its unmasked form, having regained its health. Nightmare does not have the same attacks as before, but instead, will now fire three larger, slower energy blasts at a time and a laser from its face, as well as use its Gravity Manipulator to create large vortices that suck in all of Samus' beam and missile fire. While these vortices remain in the room, Samus can go to the opposite side of the room in order to damage Nightmare, as the vortex will then suck the blasts and missiles to the creature. Occasionally, the unmasked Nightmare will fall to the ground, only to rise up again. Nightmare is also much easier to deal with now that the Gravity Feature is activated. When defeated, it will explode, leaving the arms and tail shattered into pieces and the destroyed body laying on the ground, officially defeated.

The body and shattered remains of Nightmare will remain on the ground until the post-credits sequence.

Metroid Fusion
In Metroid Fusion, Nightmare has three phases, excluding its Core-X form.

Phase 1


During this phase, Nightmare will stay in front of Samus and shoot lasers from its arms at regular intervals. These lasers can be difficult for Samus to jump over as it shoots them in a spread. Its weak point is the gravity manipulator - the glowing purple protrusion connected to its central body. Normally, its arms will be blocking it, so Samus must lure Nightmare up by jumping high, then coming down and getting a shot or two at it using the charged Plasma Beam or an Ice Missile. Once it has been sufficiently damaged, the battle enters its second phase.

Alternatively, Samus can stay under Nightmare in its first phase, as the creature only stays in one spot while hovering horizontally, and whenever Nightmare would come down, Samus could roll into a Morph Ball and stay out of harm's way, then come back and shoot the manipulator with more missiles and charged shots.

Phase 2


Nightmare's gravity manipulator activates, weighing Samus down and making her Missiles drop mid-flight, forcing Samus to rely on her charged Plasma Beam, or hit with missiles point-blank. Nightmare will begin to move slowly back and forth, and a slimy, green substance begins to ooze from the now-open "eyes" in its face-plate. After taking sufficient damage, Nightmare's face mask and gravity manipulator both explode, returning gravity to normal.

Phase 3
Nightmare will begin to move slowly forward while firing its lasers, and then fly erratically around the room, becoming difficult to dodge. Its exposed face functions as its weak spot. Samus must utilize the ladder and the Space Jump to effectively avoid attacks and aim counterattacks. After flying around the room, it will go back to moving forward slowly and firing beams.

When Nightmare (along with its Core-X) is defeated, Samus can absorb the Core-X to restore her Gravity Suit.

Attacks
Nightmare's gravity manipulator allows it to control the gravity around it, which it puts to deadly use in combat. Using the gravity manipulator, Nightmare can increase the gravity to slow down opponents or decrease the gravity to leave opponents helpless in midair. It can also use the gravity manipulator to create large vortices to draw in incoming Beam shots and Missiles. In terms of offense, the creature is outfitted with a multi-laser system on its arms. and can shoot lasers from its mouth, as well as bombard opponents with small and large energy spheres.

Trivia

 * It is unknown exactly when Nightmare became an X-host. It can be safely said that it was uninfected before Samus acquired the Ice Missiles, as it only began flying around erratically in Sector 5 after she obtained the concussive weapon (this would also explain the seemingly senseless destruction it caused in the sector afterwards).
 * In the room that Samus confronts Nightmare in Other M, there is a mechanical device in the center of the floor that bears a striking resemblance to the Gravity Suit power-up from Super Metroid. While possibly coincidental, its appearance could be symbolic of both acquiring the Gravity Suit from Nightmare in Metroid Fusion and Nightmare's gravity-manipulating abilities.
 * If Samus shoots Nightmare's body after the second battle, her shots will pass cleanly through it, when they shouldn't because the Wave Beam in Other M can only shoot through transparent objects.
 * In Fusion, the boss is found inside a room in which the background is composed of scraps of metal, machinery and cables. Whether or not Nightmare caused this mess is unknown. Metroid Prime and Metroid Fusion: Prima's Official Strategy Guide calls the room an "electronic junkyard".
 * There is an enemy in the Nintendo DS game, Mario & Luigi: Partners in Time called a "Snoozorb" which is similar to Nightmare.
 * Unlike the Nightmare-X in Metroid Fusion, the original Nightmare's face in Other M does not leak out of its mask, nor does its face melt when fired at the unmasked figure.
 * It would seem the X Parasites are capable of taking the shape of inorganic materials, as Nightmare's main metallic body is revealed to be part of the Core-X and regular X during its death animation in Fusion. Based on Samus' final battle with the SA-X, the X uses organic material and molds it in the shape of artificial components that the species cannot directly infect/possess.
 * In Other M, Nightmare's destroyed body and shattered pieces are not the only remains that disappear after the post-credit sequence. Ridley's clone's body vanishes after the credits and reappears in Metroid Fusion, having also been transported into the BSL station by the Galactic Federation.
 * The Nightmare's first form in Other M shares its theme with Goyagma.
 * With no fewer then two health bars ,Nightmare has the most health out of all the bosses in metroid other m (unless Nightmare's two forms are considered separate bosses).