The Black Arms are a demonic alien race led by Black Doom. They appear in the game Shadow the Hedgehog, in which they invade Earth in search of the seven Chaos Emeralds, and are opposed (or aided) by Shadow the Hedgehog and other characters.
They want to use the Chaos Emeralds to manipulate space and time and warp the Black Comet down to Earth. They plan to enslave and subjugate humanity, turning them into a renewable food source.
Eventually, the Black Comet was destroyed when Shadow the Hedgehog fired the Space Colony ARK's Eclipse Cannon directly into the comet, presumably rendering the race extinct.