Dark Samus

Dark Samus is the main antagonist of the Metroid Prime series debuting in Metroid Prime 2: Echoes. Dark Samus is a form of Metroid Prime, created after it merged with Samus Aran's Phazon Suit in order to survive.

Super Smash Bros. Brawl
In Super Smash Bros. Brawl, Dark Samus does not appear in a physical form, though she still has both a collectible trophy and a sticker, both depicting her appearance in Metroid Prime 2: Echoes. In Subspace Emissary, her sticker can only be equipped by Samus and Zero Suit Samus, and gives them an increase in their battering resistance when equipped.

A "Dark Samus" appears in co-op Event 7: Battle of the Dark Sides, though while it is meant to represent this character, Dark Samus's appearance is merely Samus's model recolored to be completely black.

Super Smash Bros. for Nintendo 3DS / Wii U
Dark Samus appears as an Assist Trophy in Super Smash Bros. for Nintendo 3DS / Wii U using her appearance from Metroid Prime 3: Corruption. She attacks using a variety of Phazon-based abilities, such as tentacles that sprout from the ground, a burst of shots from her arm cannon, or spherical missiles that home in on enemies. If enough damage is dealt to her, a ball of light forms around her before she disappears; otherwise, she simply disappears after a period of time. Dark Samus is also the basis for one of Samus' alternate colorations.