Races and battle can be customized in every aspect, and players can try to earn cards by completing challenges.

The cards themselves contain art from various older Sonic games, and can unlock things such as alternate suits for the characters.

In the story mode, the races may be substituted with single character missions such as "Time Attack,” "Collect X Rings,” and other challenges.

King of the Hill has an Omochao stationed at the top of the level with a light beam.

For example, Shadow's "Chaos Control" move has the ability to slow down the other player's movement for a few seconds.

The character roster is split into teams of two (Sonic and Tails; Shadow and Metal Sonic; Silver and Espio; Knuckles and Rouge), with each team having its own story campaign that tells the events of the game's story from their perspective.

They discover that Doctor Eggman has stolen the Chao and concealed them inside a haunted mansion.

However, as he needs the seven Chaos Emeralds to open the portal to the Ifrit's dimension, he secretly hires Rouge to collect them.

Espio, having been hired to investigate the disappearances, initially believes Silver is taking the Chao for nefarious purposes, but agrees to join forces after discovering his true motivations.

Shadow and Metal Sonic set out to retrieve the Chaos Emeralds before Nega does.

Shadow and Metal Sonic close the portal, trapping themselves and Eggman Nega in the Ifrit's dimension.

However, Metal Sonic reveals the seventh Chaos Emerald inside his chassis, and Shadow uses it to teleport them back to their dimension, leaving Nega behind.

Silver returns to the future, hoping things have been made right, while Espio is left to report to Vector on the state of the case.

[2] In March 2009, Sonic Rivals was certified as part of Sony's Greatest Hits budget line, representing North American sales of at least 250,000.