You were in South Island, having just taken down the "Triple Trouble" of Fang the Hunter, Dr. Eggman, and Knuckles (actually Metal Sonic in disguise), but, right as you saved the real Knuckles, Metal Sonic sweeps down again, and knocks the Chaos Emeralds out of your hands! Using his powers, he managed to copy them into "Dark Emeralds", using them to turn into a new, almost spaceship-like form. You, naturally, chase after him, and after a brief scuffle in the air, Metal Sonic absorbs the junk around him to turn into a new, radically different form: One that is much taller, with a red color scheme, drill hands, and protruding chest. Good luck on taking him down!