The Paralyzer is Zero Suit Samus' Standard Special Move in Super Smash Bros. Brawl. Its main purpose is to stun opponents, but it also deals some damage.
Overview
It can also be charged to increase the time an opponent is stunned as well as slightly boost its range.
The Paralyzer is also used in her Down Smash, fired downwards right in front of her, and retains the stunning effect for a longer period of time.
Interestingly, the stunning effect caused by the Paralyzer is not affected by knockback resistance. Also, hitting a non-flinch character like Porky with this will cause them to shake like being paralyzed, though they will continue to move unhindered.
Origin
In Metroid: Zero Mission, Zero Suit Samus' role in the game is a stealth role; even with a charge shot, the best she can do with her gun is paralyze Space Pirates for a few seconds if it was shot when fully charged.