The Egg O' War, formerly known as the Wily Egg, is a battle station made by the teamwork of both Dr. Eggman and Dr. Wily in the Sonic the Hedgehog and Mega Man comic crossover event, Worlds Collide. It resembles the Death Egg but it has a skull insignia on it, making it a direct combination of Dr. Eggman and Dr. Wily's insignias. In the Pre-Super Genesis Wave timeline, it served as Drs. Eggman and Wily's base and key components in their plans to conquer their world by reshaping reality. When the doctors were defeated, the battle station ended up in the Sol Zone in the Post-Super Genesis Wave timeline, where it was repaired and renamed the Egg O' War.
The Wily Egg was created in the Skull Egg Zone after Dr. Eggman and Dr. Wily met each other and began working in the zone. Eggman provided the Wily Egg with its primary design due to his experience of building battle stations, and Wily handled the details due to his flair for internal defenses.
After finishing it, the doctors christened it the Wily Egg, after having a compromise about the name, as Eggman wanted to call it the "Death Egg III" and Wily wanted to call it "Wily Flying Fortress". From within the Wily Egg, the doctors then put their plan into motion by unleashing the Genesis Wave upon both Mobius Prime and Earth 20XX, reshaping and rewriting both realities to their benefits.
Eventually after many battles, Sonic and Mega Man managed to get inside the Wily Egg. Upon their arrival, they faced off against Metal Sonic and Bass and managed to defeat them. After a titanic battle with the doctors and the firing of the Super Genesis Wave, reality went back to normal and the Wily Egg was presumed to have been erased.
The Wily Egg ended up in the Sol Zone in the Post-Super Genesis Wave timeline. It was found by Captain Metal, who remodeled it into the Egg O' War. Captain Metal planned to use the Sol Emeralds in order to power the Egg O' War.
After his body was destroyed by Burning Blaze, Metal revealed that he had downloaded himself into the Egg O' War, essentially becoming it. He then fought Blaze but was sunk by a massive flame beam. However at the ocean floor, Captain Metal came back online.