From Sonic Retro
The Cacophonic Conch is an item that appears in Sonic Lost World. It is a very rare conch shell based on a real-life musical conch. When blown into, the conch produces a low-pitched sound that affects a nearby Zeti, naturally inhibiting their powers, but causing them great pain in the process as the frequencies it emits are very excruciating to them.
Prior to the events of the game, Dr. Eggman acquires the conch from an unknown location and uses it to enslave the Deadly Six. Whenever the Zeti fail to do a good job or try to speak up against him, he inflicts pain on them as punishment. When he tries to punish the Zeti for their failures at Desert Ruins, Sonic intervenes by kicking away the conch into the distance, never to be seen again for the rest of the game. This would be a terrible mistake, as it allows the Deadly Six to take control of Eggman's Badniks and rebel against the doctor.
It is implied that more than one Cacophonic Conch exists in the world, as Eggman vows to find another one to take the Deadly Six under his control again at the end of the game. However, the Japanese script suggests that the conch may be the only one of its kind as Eggman does not mention there being another.
In other media
In the Sonic the Hedgehog comic series and its spinoffs by Archie Comics, the Cacophonic Conch was acquired by Dr. Eggman at some point before the Worlds Unite crossover to enslave the Deadly Six and find a different approach to the Shattered World Crisis. However, the conch was destroyed behind his back by Sigma, who was possessing Orbot. After the events of Worlds Unite were erased and after reclaiming Eggmanland in the events of "Eggman's Dozen", Eggman assigns Wendy Naugus with searching for a Cacophonic Conch after recruiting her as one of the Egg Bosses.
In the Sonic the Hedgehog comic series by IDW Publishing, the Cacophonic Conch is referred to as the Cacophonous Conch. Dr. Starline, due to being an avid collector of Eggman's paraphernalia, had found the conch using the Warp Topaz and retrieved it after making arrangements with the Deadly Six, and attempted to use it to command the Zeti after inviting them on-board the Faceship. However, the effects quickly wore off after Starline had stopped blowing, and the Zeti took the conch away from him while his guard was down.
The conch was last seen lying on the ground among the wreckage of the Faceship after it crashed in issue #28.