Sonic Rivals
After a mysterious desturbance, a new island Onyx island appears, many of the rivals friends are turned into cards, now the rivals must battle what is belived to be Dr. Eggman and even worse, each other!
Miles "Tails" Prower: Upon journeying to Onyx Island with Sonic, Tails is turned into a card by Dr. Eggman's camera as proof to Sonic that he indeed has the power to do so. It is now up to Sonic to save both him, and Amy, who has also been turned into a card. He appears as a playable character in the sequel, Sonic Rivals 2.
Amy Rose: The first to be turned into a card after Eggman, Sonic and Tails' journey to Onyx Island to discover this shocking truth. After Tails himself gets turned into a card, Sonic sets out to save them both.
Rouge the Bat: After discovering the truth about "Dr. Eggman", Rouge goes missing, but it is later revealed that she was turned into a card. Shadow sets out to save Rouge while trying to figure out what she had discovered. She appears as a playable character in the sequel, Sonic Rivals 2.
Spoiler:
Dr. Eggman: Eggman, in fact, is not the troublemaker in this story. He is actually the victim. He was the first to be turned into a card by his doppelganger Eggman Nega before the main storyline actually occurs.
Spoiler:
Eggman Nega: As it turns out, Eggman Nega is the main antagonist of the game, who hails from the future. Masquerading as Dr. Eggman in the past, he uses a special camera to turn everyone into cards on Onyx Island, an island he brought along with him from the future. His master plan is to change his destiny by turning the whole planet into a card that he can control, he gets turned into a card, and Silver departs with him and the island.
Sonic Rivals 2
Spoiler:
The Chao have gone missing and Sonic the Hedgehog and Miles "Tails" Prower immediately get on the case to find them. It turns out that Eggman Nega (once again masquerading as Eggman), has stolen the Chao and hidden them inside a haunted mansion. His plan is to feed them to an inter dimensional beast called the "Ifrit" who needs to eat them to become invincible. After that, he plans to release the Ifrit into the world in order to destroy it. However, to open the portal to Ifrit's world, the seven Chaos Emeralds are required. Eggman Nega thusly hires Rouge the Bat to collect the Chaos Emeralds. The Master Emerald has also gone missing (again) and Knuckles the Echidna teams up with Rouge to find it.Meanwhile, Silver the Hedgehog has returned from a now ruined future caused by the Ifrit. In order to make a new future, he steals the Chao that are left in order to hide them. He crosses paths with Espio the Chameleon, who is also on the case of the missing Chao, and they work together to save the world. The real Dr. Eggman sends Metal Sonic to find Shadow the Hedgehog, and lets them know of Nega's plans. Nega has learned of the Ifrit by accessing Professor Gerald Robotnik's journals, and Shadow and Metal set out to get the Chaos Emeralds before he does. Eggman uses Metal Sonic as a communication device to aid Shadow along the way.
All of the teams meet up at the Mystic Haunt Zone where the portal to Ifrit's wold is. Despite Rouge only collecting six of the Emeralds, the portal opens anyway and Nega dispatches his new Metal Sonic version 3.0 to awaken the Ifrit. Despite possessing Sonic, Tails, Knuckles, and Rouge, the Ifrit is defeated by the other teams. Shadow and Metal Sonic close the portal and seal themselves and Eggman Nega in Ifrit's dimension. Metal Sonic reveals that the seventh Emerald was stored in his chassis and he and Shadow use Chaos Control to exit that world. Nega is left trapped under some rubble.
Sonic and Tails take all the Chao to a Chao Garden, and Knuckles find the Master Emerald in the Emerald Detector he and Rouge stole from Eggman Nega. Rouge steals the Master Emerald and runs, and Silver returns to what he hopes is a happy future. Espio has to answer to Vector the Crocodile who has spent their client's advanced payment on late rental fees.