After abilities were introduced to Pokémon there was one unused ability that essentially made it into the game anyway. With so many abilities in the series, it's hard to imagine one that went by without ever being used. However, the story behind it is quite fascinating even though there is still a lot of mystery surrounding it.
Abilities were introduced in Pokémon Ruby and Sapphire, and have been a vital part of the series ever since. Every Pokémon has at least one possible ability that it can have active, and these abilities all apply an extra effect to them or their battles. For example, Pokémon with Limber are immune to Paralysis, and Pokémon with Unaware ignore their opponent's stat changes. A Pokémon's ability is important, and in some cases, such as a Weezing having Levitate to remove one of their weaknesses, it's one of their strongest assets. Keeping track of a Pokémon's ability is just as important as knowing their stats and moveset.
In Generation 3, alongside the rest of the original abilities, there was one ability called Cacophony. Cacophony's ability was identical to that of Soundproof, making the immune to sound-based moves. However, Cacophony was never used for a single Pokémon. It was removed in the very next generation, likely due to not being used for any Pokémon in the first place. This makes Cacophony the most obscure ability in the series, even more than abilities that are restricted to only one Pokémon such as Wonder Guard or Disguise. Similar to Pokémon's growing list of regional variants, abilities changed the Pokémon world in a major way, and the series is almost unrecognizable without them.
Cacophony Is Identical To Pokémon's Soundproof Ability
One would likely assume that one reason for Cacophony's removal was due to it being functionally identical to another ability, Soundproof. However, there are other instances of Pokémon abilities being identical, and neither of them were removed. For example, the Legendary Pokémon Rayquaza has the Air Lock ability, which negates all weather effects while it's in battle. However, the relatively common Psyduck's Cloud Nine ability does the same. Another example comes in the form of Insomnia and Vital Spirit, which both prevent the from falling asleep. Although there are some Pokémon abilities that could arguably be cut, the developers clearly don't mind abilities having the same effect, which makes Cacophony's removal more confusing.
There is one theory surrounding Cacophony that could have some merit. There is an Exploud card from the Great Encounters TCG set that has a move, Ambient Noise, that was known as Cacophony in Japan. This opened the theory that Cacophony was intended to be an ability for the Whismur line. Considering that Whismur, Loudred, and Exploud are all loud, sound-based Pokémon, this theory makes sense. Considering that the Whismur line all share Soundproof as an ability, which is functionally identical to what Cacophony was supposed to do, it's almost like they had Cacophony all along. Although even if this is the case, the reason for Cacophony's removal is still unclear, especially since it never even resurfaced as one of Pokémon's updated hidden abilities.
Cacophony is one of the more unusual mysteries surrounding the Pokémon universe. There is no precedent in the series for removing abilities, not even when they were first brought into the game. However, if Cacophony truly was meant to be the Whismur line's ability in Pokémon, then in a roundabout way, it still made its way into the games.
