The Poké Ball (モンスターボール, Monsutābōru, Monster Ball) is an item that, if thrown, will release one of a number of Pokémon. Each Pokémon does a different thing, including attacking the thrower's opponents, changing the properties of the stage, and inducing status effects. The Poké Balls in Super Smash Bros. release Pokémon from Pokémon Red, Blue and Yellow, while the Poké Balls in Super Smash Bros. Melee release Pokémon from Pokémon Gold, Silver and Crystal in addition to Pokémon from Red, Blue and Yellow. The Poké Balls in Super Smash Bros. Brawl also release Pokémon from Ruby, Sapphire, Emerald, FireRed, and LeafGreen and Diamond and Pearl. In Brawl, the Poké Ball makes a unique sound effect when it appears, thus alerting one to its presence even if it appears off screen.
In Brawl, the number of Poké Balls that can be on-screen at once has been reduced to 3, instead of the unlimited number of Poké Balls that could appear in Melee.
The Poké Ball is also featured as a trophy in Melee and Brawl.
In the Pokémon series, the Pokémon trainer has to capture wild Pokémon to add to his or her party Pokémon. When the Pokémon trainer encounters a wild Pokémon, he or she must use their Pokémon to weaken the wild Pokémon if necessary. When the Pokémon is weak enough, the trainer can throw a Poké Ball at it to capture it. It takes three wobbles and then a click from the Poké Ball for a successful catch. Poké Balls are also used for the storage of Pokémon. When the trainer gets in a battle, the trainer throws a Poké Ball out on the battlefield that contains the Pokémon of his or her choice and the Pokémon is released. The Poké Ball has been used in almost every Pokémon game since and functions the same. In the Super Smash Bros. series, the Poké Ball is an item that can be picked up, thrown, and release a random Pokémon (refer to the list below for all the Pokémon). 
 List of Poké Ball Pokémon
 Pokémon in Super Smash Bros.
 Pokémon in Super Smash Bros. Melee
 Pokémon in Super Smash Bros. Brawl
Note that Pokémon with a given frequency of 0 are assigned a combined 1/493 chance of appearing, independent of the rest of the frequency system. It should also be noted that at the time that this game was made, there were only 493 Pokémon, probably resulting in the variable of the Pokémon appearing.
 Description from the Super Smash Bros. Instruction Booklet
When thrown, the ball opens up, and a PokémonTM pops out. The Pokémon that appears is random; it performs its special skill then leaves.
 Trophy Info (Melee)
These balls are used to capture and contain wild Pokémon. Most Pokémon must be weakened in some way before they can be captured, but once they're inside a Poké Ball, they enjoy their new home, since Poké Balls contain an environment specially designed for Pokémon comfort. Master Balls are the strongest type.
 Trophy Info (Brawl)
An item used for capturing Pokémon and calling them out to battle. Pokémon live in these items which, despite appearances, actually contain a wide, comfortable, Pokémon-friendly world inside them. In Super Smash Bros., Pokémon give temporary support to whoever calls them out. You never know which Pokémon you'll get, but some of them are devastatingly powerful.