Selkadoom's first memories were from when Shadow was created. He was just floating around, gaining knowledge about the world. It was like that until Dr. Eggman appeared. He built a spare body for Shadow, in case something went wrong. Selkadoom thought it was his chance and he possessed the spare body. Then, he annihilated Eggman.

After that, Selkadoom started looking for Shadow. He wanted to make him an ally. He thought of himself as Shadow's dark twin. Selkadoom tried to convince him to cooperate. He was in a dilemma. A half of his body turned black. But Sonic and his friends got in the way. They kept him on their side. Selkadoom started fighting Sonic and the gang.

They almost defeated him, but they didn't know he had a trick up his sleeve. Selkadoom had built the Machine of Doom. It looked like a slot machine with an ominuous blue lamp serving as her eye. The Machine randomly generated "programs" and attacked by turning her opponents into objects or giving them various effects. The Machine turned Sonic into a werehog, Tails into a rainbow no-brainer, Knuckles's body into a pile of steel and Shadow into an electrified version of himself.

But the team still somehow managed to destroy the Machine. Selkadoom was cornered. The gang didn't kill his physical body, though. Sonic and friends pushed him and the Machine's remains through the portal to some desert. Then, they closed the portal. Makind the demon stranded on an outback made them feel safe...