In the Pokémon series, the Master Ball is one of the rarest Poké Ball variants, and the most powerful. Whereas all other Poké Ball variants may fail at capturing a wild Pokémon under certain circumstances, a Master Ball will catch any wild Pokémon without fail, regardless of their health and status. Legendary Pokémon are typically much more difficult to capture than most other Pokémon due to having very low catch rates, and are thus a prime target for a Master Ball. However, contrary to its depiction in Smash, most Mythical Pokémon (such as Arceus, Marshadow, and Genesect) cannot be legitimately found in a Master Ball; as they are event Pokémon, they can only be received in the special, all-red Cherish Ball.
Usually, only one Master Ball is obtained per save file, but they also appear as rare prizes from lottery minigames. The Master Ball is typically obtained from a character in the story at some point prior to encountering the game's main Legendary Pokémon.
Like the Poké Ball, the Master Ball releases a Pokémon when thrown, but unlike the ordinary Poké Ball, it is almost guaranteed to release a Legendary or Mythical Pokémon. The only exceptions are the dud Pokémon Goldeen, which deals no damage, as well as Zoroark, who is not officially considered Legendary or Mythical, but was event-exclusive at the time of its release, much like most Mythical Pokémon. Legendary Pokémon can appear from both types of Poké Balls, but a Master Ball is far more likely to contain them. Similarly-functioning Poké Balls previously appeared in Super Smash Bros. Melee in Event 37: Legendary Pokémon.
List of Master Ball Pokémon
Pokémon in this table are listed by their order in the National Pokédex.