In the Pokémon universe, Poké Balls are used to catch and store Pokémon.
Poké Balls in Super Smash Bros. Ultimate are special items that, when thrown, release a randomly selected Pokémon. The released Pokémon activates a unique power that affects the battlefield and its combatants. Some Pokémon unleash an area-of-effect attack, some perform attacks against the summoner’s opponents, and some Pokémon can produce effects that harm everyone, including its summoner (the player who picks up and uses the Poké Ball).