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The Time Gears are artifacts of great importance in Pokémon Mystery Dungeon: Explorers of Time and Explorers of Darkness and Pokémon Mystery Dungeon: Explorers of Sky.
The Time Gears help keep control of the flow of time in the Pokémon world. Even the most hardened criminals know not to disturb the Time Gears, lest the proper flow of time be disrupted. However, a mysterious thief starts to steal them over the the course of the storyline, causing time in those areas to stand still.
The thief is found to be Grovyle, and the player eventually brings him to justice. The stolen Time Gears are then returned to their respective areas. However, it is revealed that Grovyle stole the Time Gears to prevent an even greater catastrophe: the paralysis of the planet. The frozen time would be only temporary until the Time Gears were placed in Temporal Tower, where the flow of time would be fixed for good.
When the player and Grovyle go to Treeshroud Forest to take the first Time Gear, time has already frozen. Acting fast, Grovyle obtains the rest of the Time Gears and the party goes to Temporal Tower. Grovyle throws himself and Dusknoir, their pursuer, into a portal going to the future, while he entrusts the five Time Gears to the player. Together, the player and partner place the Time Gears in the slots at the top of the tower and prevent a future of darkness.
In the anime
A Time Gear appeared in Pokémon Mystery Dungeon: Explorers of Time & Darkness being stolen by Grovyle.
In Pokémon Mystery Dungeon: Explorers of Sky - Beyond Time & Darkness, Grovyle gave three Time Gears to Team Poképals when he was about to go back to the future.