The Zero Suit is a blue, form-fitting body suit, worn underneath armor like the Power Suit or Varia Suit. This suit first appeared in the Game Boy Advance title Metroid: Zero Mission, from which it took its name, and in which she temporarily loses her power suit and all of its weapons and abilities, and must infiltrate an ancient Chozo temple in order to acquire a new one. In previous Metroid titles, if the player beat the games under a certain time or with a certain number of items collected, the player would be rewarded with a brief scene depicting Samus in attire that varied from game to game. However, all Metroid games released after Zero Mission depict the Zero Suit as Samus's standard attire worn under her suit. During the Zero Suit gameplay segment of Metroid: Zero Mission, Samus's defense is much weaker, causing her to take more damage from enemy attacks. Her only weapon is an emergency pistol that can stun - but not kill - Space Pirates, and without the Morph Ball power, she must crawl through narrow passages on her hands and knees.
Super Smash Bros.
In Super Smash Bros. Brawl, Samus is able to transition between her Power Suit and Zero Suit during play. Zero Suit Samus, as she is called in the game, is more agile than when armored. She is also able to run faster and jump higher, but her lightened weight also makes it easier to K.O. her. Solid Snake's Easter egg CODEC conversation with Mei Ling regarding Zero-Suit Samus indicates that Samus has superhuman abilities due in part to her extensive training with the Chozo race, though traditionally it is actually because of a blood transfusion from the Chozo to help the human survive on their homeworld.
The Zero Suit also makes appearances as an unlockable costume in Fatal Frame IV, Dynasty Warriors Vs., and Tekken Tag Tournament 2: Wii U Edition.