Cog

A Cog is an item that first appeared in Donkey Kong Country 3: Dixie Kong's Double Trouble!. There are five Cogs in all, and each one is critical in raising the Knautilus.

Whenever Dixie and Kiddy Kong clear a level for the first time in Krematoa, they will receive a Cog upon raising the level's Level Flag. While the Kongs have no real use for any of the Cogs, by taking them to Boomer, he will insert them into a strange machine in his bomb shelter. Although the Cogs will apparently do nothing at first, once all five of them are inserted into Boomer's machine, they will reawaken the dormant volcano within Krematoa, and, more importantly, trigger the Knautilus into rising from Krematoa's lake.

Another Cog could be found in the X-Naut Fortress in the game Paper Mario: The Thousand-Year Door. It's on top of a shelf in the room with the Yux experiments. Mario reaches it by going through a vent.

Return it to the prize-grabber crane machine on Sublevel 1, then press the left, right, and middle buttons in that order to activate the crane. The crane is in a strange room with fancy devices, and a platform covered in prizes.

Work the crane by pressing A to go to the left and press B to go back. The Feeling Fine badge and a Star Piece can be obtained on the platform, along with some coins.