Zero or low gravity is an obstacle that presents itself in Metroid: Other M and Metroid Fusion. It drags down Samus Aran's movements, making her move slower and her weight heavier, or be flipped upside down. The only way to negate abnormal gravitational fields is by acquiring the Gravity Suit.
In Other M, extreme gravity is found in the corridors in the direction of Sector Zero in the Cryosphere. Rooms bogged down by gravity have a noticable purple hue. This area contains two Missile Tanks and an E-Recovery Tank, which are difficult or impossible to acquire until the Gravity Feature is activated. In Fusion, when in low gravity the room has a wavy, mirage effect.
The ability to manipulate gravity is associated with Nightmare, a mechanical bioweapon that Samus faces in both Other M and Fusion. Nightmare is likely the cause of the low gravity in the Cryosphere, but defeating it does not return the gravity to normal. Nightmare uses its gravity manipulation abilities, which stem from its "tail", as a weapon in battle, causing long-range Missiles to fall to the ground and dragging down Samus' movements. The only effective method of attacking the tail is by shooting it with the Plasma Beam or point-blank Missiles (in Fusion only). In Other M, the Plasma Beam is stacked along with the Ice Beam, allowing Samus to freeze the tail over. This buys her time to attack Nightmare's face until it breaks its tail free from the ice. After Samus escapes Sector Zero, she must fight Nightmare again, but has the Gravity Feature activated, allowing her to move easier.
A hazard related to gravity is the lack of any gravity altogether. In Other M, this is seen when Samus is escaping Sector Zero. The entrance corridor she is escaping from begins to detach in sections, and though Samus tries to keep running, she is eventually sucked out into space, forcing her to activate the Gravity Feature to save herself. When she eventually battles Phantoon, the ethereal behemoth smashes through the windows in the Control Bridge, creating a vacuum into space. Since the Gravity Feature is active at this point, it is not a problem for Samus.
The original Fusion trailers featured Samus walking on the ceilings and walls, similar to Other M.