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This article contains plot details.
At the beginning of the game, Dr. Eggman turns Miles "Tails" Prower, Amy Rose, Rouge the Bat, and the Master Emeralds into cards. Arriving on the scene, Sonic the Hedgehog and Knuckles the Echidna figure out what happened. Knuckles, being bent on saving the Master Emerald, tells Sonic that teamwork is out of the question. Sonic replies that he likes a good challenge.
Elsewhere, Shadow receives a distress signal from Dr. Eggman. Just then, a hedgehog named Silver appears. Silver says that he needs to get to Dr. Eggman before Shadow does. Later on, it's revealed that Dr. Eggman is really Eggman Nega, Dr. Eggman's descendant.
After a final battle involving Sonic, Shadow, Silver, Knuckles, and Metal Sonic, Eggman Nega is defeated. His defeat reverts everything to normal. Silver then takes Eggman Nega back to the future.
The game has received mixed reviews from critics.
- In this game, it is stated that Eggman Nega is from Silver's future and that he is Dr. Eggman's descendant. However, in Sonic Rush, which came before this game, it is stated that Eggman Nega is Dr. Eggman's counterpart from Blaze the Cat's world. Its sequel, Rush Adventure, would keep with this back-story while Rivals 2 would keep with Rival's back-story.