Zero Suit Samus
Zero Suit Samus is the title used to refer to Samus Aran while she is wearing only her Zero Suit. Zero Suit Samus first appears at the final stages of Metroid: Zero Mission. She also appeared as a playable character in Super Smash Bros. Brawl, and will be playable in the upcoming Super Smash Bros. Wii U and Super Smash Bros. 3DS games.
Metroid: Zero Mission
In Metroid: Zero Mission, Samus loses all of her abilities after fighting Mother Brain, leaving her stripped down to the Zero Suit and an Emergency Pistol. Equipped with only these most basic items, Samus manages to traverse the Space Pirate Mother Ship and reclaim her old abilities along with new ones (the Gravity Suit, Plasma Beam, and Space Jump). This expanded suit is commonly known as the Legendary Power Suit.
Metroid Prime Series
Samus appears briefly in her Zero Suit in the ending sequence cutscenes in Metroid Prime 2: Echoes and Metroid Prime Hunters, and in the opening and ending sequences in Metroid Prime 3: Corruption. At no point is she playable without her Power Suit in any of the Prime games, however.
Metroid: Other M
Zero Suit Samus is first shown in a cutscene in which Samus is being rehabilitated after her return from planet Zebes before beginning training. She appears in another cutscene after she is knocked unconscious by Adam Malkovich to prevent her from entering Sector Zero. After defeating Phantoon, Samus finds Adam's helmet and deactivates her Power Suit. A countdown is started, and Samus must escape the Bottle Ship clad only in her Zero Suit and armed only with the Paralyzer.
Super Smash Bros. Brawl
Zero Suit Samus is notably more agile but weaker than other characters. When she is obtained, her speed makes dodging and landing hits easy, but at the price of lowered offensive capabilities. Her recovery is excellent, but not the best, as those spots are occupied by flying characters.
Zero Suit Samus can be chosen at the start of a match on any mode by holding down the shield button (variable depending on the controller choice, Z on a default Nunchuck/Wii Remote set) and choosing "Start" (+ on the Nunchuck/Wii Remote set). Additionally, during a match of any sort (excluding the Subspace Emissary) Samus and Zero Suit Samus can switch freely between each other by repeatedly Up-taunting then Down-taunting rapidly. This is known as a Smash Taunt. 
Zero Suit Samus's Moveset
- Special Move: Zero Suit Samus's Special Move fires her Paralyzer Weapon. It is a short ranged, yet useful weapon that paralyzes the opponent.
- Side Special Move: Zero Suit Samus's Side Special Move is her Plasma Whip, which whips the enemy with a beam from the Paralyzer, causing minor damage.
- Up Special Move: Zero Suit Samus's Up Special Move is her Plasma Wire, which is basically the Plasma Whip that fires upward, and can grab on to ledges.
- Grab Move: Zero Suit Samus's Grab Move is a version of the Plasma Whip that functions the same way as the Grapple Beam.
- Final Smash: Zero Suit Samus's Final Smash restores her Power Suit, while causing damage to opponents.
Super Smash Bros. Brawl
- When a player is in the section of Metroid: Zero Mission where Zero Suit Samus is playable, Zero Suit Samus's face, rather than a helmeted Samus, will appear when choosing the file on the start screen.
Alternate Brawl Costumes
- Smash Dojo
- "Samus Aran without her mighty Power Suit. In this condition, she does not have the firepower she's famed for but is in full possession of the agility and athleticism she gained through her childhood training with the Chozo. Without the armor, she's also much, much faster. The weapon she carries is a self-protection device known as a Paralyzer that stops enemies cold." —Zero Suit Samus Trophy (Super Smash Bros. Brawl)
- "Zero Suit Samus's Final Smash. Samus loses her Power Suit when she fires the Zero Laser, but she can restore it — that is, she can return from her Zero Suit form to her familiar armored form. That being said, Zero Suit Samus is very quick with great reach, so there are tactical reasons to fight as is. If that's your preference, don't pick up any Smash Balls." —Power Suit Samus Trophy (Super Smash Bros. Brawl)