Prof. Gerald had created the Ultimate Life Form. Gerald secretly used the ARKs' power to transport Sonic and the others to Earth to confuse them.
Prof. Gerald decided to test Shadow's new strength on his prototype, the Biolizard. Shadow used the Biolizards' attack against it. "CHAOS CONTROL!" The Biolizard got transported back to where it came from. Shadow had no idea what he had just done.
"Prof. Gerald, what did I just do?"
"You just used a technique called Chaos Control, using the power I gave you. But that power will be much greater with the power of a Chaos Emerald."
"A Chaos Emerald?"
"Yes. When I pass away, you will use their power to take over the world! That is the reason you were created."
Prof. Gerald convinced Shadow about taking over the world. He taught Shadow everything about the Eclipse Cannon and the Chaos Emeralds' power.
On his break, Shadow was looking down to Earth, dreaming of what it would be like. A 14-year-old girl came up to Shadow.
"Hello, you must be Shadow."
"Huh? Who are you?"
"My name's Maria. I'm Prof. Gerald's granddaughter."
"Tell me Maria, what is that planet down there?"
"It's called Earth. It's the planet I was born on. But I wasn't down there for long, I got sent up here with Prof. Gerald."
"……. I want to go down there someday. I feel like I've been up here for years."
"Tell you what, I promise we will go down there someday."
"Really? OK."
A few days later, some men from GUN headquarters invaded the ARK. Maria ran into the room Shadow was in and quickly locked him in a glass tube.
"Maria! What are you doing?!"
"Shadow, I'm afraid I can't go down to Earth with you. But please promise me, you'll give all those people on that planet a chance to be happy. Sayanora, Shadow the Hedgehog."
"MARIA!! NO!!!"
The last thing Shadow heard was a gunshot, as he got sent down to Earth.
Insert Sonic Adventure 2 Battle and Sonic Heroes here
Note: When Sonic and Shadow saved the Earth, they all got transported back to Mobius