From Sonic Retro
Cosmic Fall is a level in the game Shadow the Hedgehog (game). As the Black Arms proceed to attack the Space Colony ARK, its structural integrity is compromised and everything is beginning to go to pieces as Shadow arrives on the scene. While outside platforms disintegrate and plummet towards the Earth, sirens wail throughout the interior corridors. Though everyone on board has fifteen minutes to vamoose, Doom's Eye and Vector still have business to attend to and would appreciate your assistance.
Squish all the Artificial Chaos jellies in Lost Impact or nab the Chaos Emerald in Space Gadget to arrive at Cosmic Fall. Shortly thereafter, Doom's Eye asks you to retrieve a Chaos Emerald located in the ARK's power plant. As you enter the first interior area, Vector desperately wants your help in finding the computer room. What objective you choose ultimately depends on what actions the player takes in the final room of the power plant. Fall from the doorway to the floor and you'll be forced to complete the dark mission. If you so fancy, you can also triangle-jump across breakable panels(or lightspeed dash through some rings activated by a switch behind the locked gate) to elevated platform on the other side, from which you can traverse one more section of crumbling debris before finding the computer room and completing Cosmic Fall's heroic mission.
Settle for the dark mission and Dr. Eggman pops up with his Egg Dealer, determined to stop Shadow from tarnishing his granddaddy's legacy. After summarily trashing the Doctor's machine, Shadow gathers all seven Chaos Emeralds, concludes that he is the ultimate lifeform created by Dr. Gerald Robotnik and takes up the helm as the ARK's guardian. The cantankerous Eggman is allowed live, on the condition that he never again sets foot aboard the space station again. Screen fades, credits roll.
Go the extra distance to complete the hero mission and Black Doom manifests himself, chastising Shadow for blatantly ignoring his previous orders. A scuffle between the two ensues, with Vector fighting on your side, for what it's worth. Shadow emerges victorious and gathers all seven Chaos Emeralds. A crippled Black Doom promises that his forces will rise again, but Shadow ignores him and makes a dreary monologue concerning himself as a disastrous military experiment that never should have been created. As Shadow mopes off, Vector makes a feeble attempt to cheer him up, raising the possibility that Shadow's purpose was misidentified. Screen fades, credits roll.