Paralyzer

The Paralyzer is an emergency weapon that appears in Metroid: Zero Mission and Super Smash Bros. Brawl. It is chiefly used to stun enemies.

In Zero Mission
When Samus Aran's gunship crashes on planet Zebes, she is not able to use her suit. Thus she is left with only her (then unnamed) "rather useless emergency pistol". It is listed just as "Pistol" in the equipment screen. It will automatically charge itself and fully charged shots will stun the Space Pirates long enough for Samus to run and hopefully escape or hide. It is also used to defeat the Chozo Hieroglyphic. This last-resort weapon becomes her only defense and lifeline in the raid against the Space Pirate Mothership.

In Super Smash Bros. Brawl
First referred to as Paralyzer in the trophy description in Super Smash Bros. Brawl, Zero Suit Samus uses this as her main weapon in this game. It can be used to stun enemies in a similar fashion to how it is used in Zero Mission. A new feature not seen in the previous game in which it appeared is the ability to transform it into a whip to attack enemies and set them up for combos. Because of this function it replaces the grapple beam used when Samus has her Varia Suit. It can also be used to tether onto edges.