From Bulbapedia, the community-driven Pokémon encyclopedia.
Cacophony is an ability introduced in Generation III (unused and thus dropped in Generation IV), that avoids sound-based moves. This ability is identical to Soundproof, but only usable in Generation III games.
Cacophony is an ability coded in the Generation III games, but no Pokémon have it. It can be acquired by hacking the game or using a cheating device. Since no Pokémon have the ability by normal means, it was removed from the coding of the Generation IV games.
Pokémon with the abiliy Cacophony are immune to the following moves.
Pokémon with Cacophony
No Pokémon have Cacophony as their only ability.
No Pokémon have Cacophony as one of their two abilities.