Black Gears
From Multiversal Omnipedia
Creations of Devimon, the Black Gears could enter the body of a Digimon and turn them into an evil slave of their creator. When more than one entered a slave Digimon (or Devimon himself), they could also infuse them with dark energy and increase their strength.
The Black Gears were not used after Devimon's defeat, although the Digimon Emperor's Dark Spirals were fairly similar.
