Mother Brain is a recurring antagonist of the Metroid series, and a major leader of the Space Pirates. She appears in Metroid (and its remake Zero Mission), Super Metroid, and in a flashback sequence in Metroid: Other M.
In Metroid, Samus had to fire missiles to create an opening in Mother Brain's Control Capsule, then continue to fire missiles through that opening to damage Mother Brain while avoiding enemy Rinkas. In Super Metroid, the first half of the battle is similar to the battle in Metroid. After Mother Brain is seemingly defeated in Super Metroid, she transforms into her bipedal form with a mechanized body, and she also opens her eye. Towards the end of the battle, she will fire Laser Brain Attacks from her eye that almost kill Samus before being saved by a Metroid. In the Metroid remake, Metroid: Zero Mission, the battle is identical to how it was in Metroid, except after the Control Capsule is broken, she opens her eye and fires blasts from it. Although Mother Brain herself is absent in Metroid Dread, brain mechanisms similar to Mother Brain appear in the game along with enemy Rinkas.
Overall, Mother Brain's appearance in SSB4 and Ultimate is based off her appearance in Metroid: Zero Mission, as her Control Capsule is damaged and she has her eye opened; however, the Laser Brain Attack she uses originates from Super Metroid, but was only used in her mechanized bipedal form.
Mother Brain is mentioned in the opening narration of Opening/Menu (Metroid Prime), which refers to her defeat during the events of Metroid and Zero Mission.
Mother Brain appears as a sticker in Brawl.
As an Assist Trophy
Mother Brain appears in Super Smash Bros. 4 as an Assist Trophy. She uses her signature Laser Brain Attack when summoned, and is guarded by Rinka enemies. She can be killed by hitting her from behind after the Control Capsule's glass shatters following the laser blast.
Mother Brain stands as potentially one of the most damaging Assist Trophies in the game, as her Laser Brain Attack can do up to 90% damage if all hits connect, and will guarantee a shield break if an enemy decides to shield it. Despite such, it only does moderate knockback.
As an Assist Trophy
Mother Brain returns as an Assist Trophy in Super Smash Bros. Ultimate, seemingly without any change in function. However, KOing her will now earn a point. Training Mode describes her Assist Trophy: Shoots a powerful beam from her eye. Rinkas help her out. She cannot appear in Luigi's Mansion, Pac-Land, Rainbow Cruise, Spirit Train, The Great Cave Offensive, Tomodachi Life, Tortimer Island, and Umbra Clock Tower
In Adventure Mode: World of Light, Mother Brain is presumably one of the countless spirits captured by Galeem during his takeover of the universe. After Galeem's defeat, Dharkon takes control of Galeem's spirits, including Mother Brain. After Dharkon's defeat, he flees to the final world, with Galeem following soon after. In the final world, Galeem and Dharkon wage war against each other using their captured spirits, with Dharkon taking control of Mother Brain.
Mother Brain's Spirit Board uses a Dark Samus puppet fighter and is fought on the Brinstar Depths stage's Ω form. During the battle, Mother Brain appears as a hostile Assist Trophy while Dark Samus' energy attacks have increased power, referencing Mother Brain's Laser Brain attack, which she uses in her second form.
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