Grim Zone

The Grim Zone is the home of Metamorphia. It is a dark and decaying town, devoid of all sunlight (despite apparently bordering on the Emerald Hill Zone), and with rivers of flame. Metamorphia lured Sonic to this Zone, where he was attacked by Troopers. Revealing herself as a shapeshifter, she incapacitated Sonic by transforming into knockout gas, then trapped him in a Retro Block. Sonic managed to escape, and defeated Metamorphia.