The Black Comet was a celestial object and the mobile homeworld of the Black Arms led by Black Doom. The comet is capable of traversing the galaxy, allowing the Black Arms to attack and consume the populations of worlds they come across.
The comet approached Sonic's World fifty years ago, and Black Doom contacted Professor Gerald Robotnik and aided him with his Project Shadow, with Doom planning to use Shadow the Hedgehog as an agent. However, The Black Arms were defeated upon their return to Sonic's world by Shadow, and the Black Comet was destroyed by the Eclipse Cannon of the Space Colony ARK. Eventually, a second comet later entered the planets orbit during the Shattered World Crisis, but it too was destroyed by a nuke. (SU: #59, #62)
- The events of the comics in both continuities seem to indicate that the Black Arms are capable of steering their comet home worlds to some degree, as the Black Comet did not simply return to Mobius/Sonic's World 50 years after Shadow's creation as it seemed to do in the Shadow the Hedgehog game.