The Egg Destroyer is the fifth and final boss of Sonic Rivals. At the end of the Meteor Base, Eggman Nega (still disguised as the normal Eggman in Knuckles and Sonic's stories) has strapped his two-dimensionalising camera to a giant spacecraft. Fueled by the cards of Amy Rose, Rouge the Bat, and the Master Emerald, he's set to destroy the world by taking a picture of it with the camera.
Unlike the other bosses of the game, this battle is fought on a linear course, along the spine of the rocket ship. Players must make their way to the front of the ship where "Eggman" is seated. Along the way they are greeted by laser cannons, freezing blasts, and fireballs, at the same time having to contend with attacks from Metal Sonic. Each section is blocked off by a laser fence which must be destroyed before it can be passed. The first hit on it sends players back to the starting point of the section; the second allows progress onwards.
As each turret is destroyed, the part of the rocket it was on detaches and explodes. Metal Sonic is teleported to the next section. Waiting at the end of the ship is Nega's control module. After two hits (bringing the total to eight hits across the Egg Destroyer as a whole), Nega's pod is sent airborne where it explodes. This explosion causes his camera to backfire, and Nega himself is turned into a card.