Sonic Rivals

Metal Sonic

Successfully complete the game with Sonic, Knuckles, Silver, and Shadow to unlock Metal Sonic. Alternately, collect the "Metal Madness", "Metal Overlord", and "Neo Metal Sonic" cards.
Knuckles' leather shoes

To get Knuckles' leather shoes, get the Buzzer 2002, Coconut 2002, and Turtloids 2002 cards.
Silver's leather shoes

To get Silver's leather shoes, get the Chaos 2 (1998), Chaos 4 (1998), and Chaos 6 (1998) cards.
Sonic's ice suit

To get Sonic's ice suit, get the Miles "Tails" Power 2002, 2004, and 2005 cards.
Sonic's leather costume

To unlock Sonic's leather suit, get the Sonic The Hedgehog, Sonic The Hedgehog 2, and Sonic The Hedgehog 3 cards. To unlock the gloves, get the Cream The Rabbit, Cheese, and Cream and Cheese cards. To unlock the shoes, get the Sonic and Amy, Amy Rose 2004, and Amy Rose 2005 cards.
Skins

Successfully complete the indicated task to unlock the corresponding character skin:
Knuckles: Successfully complete Story mode with Knuckles.
Metal Sonic: Successfully complete Story mode with Metal Sonic.
Shadow: Successfully complete Story mode with Shadow.
Silver: Successfully complete Story mode with Silver.
Sonic: Successfully complete Story mode with Sonic.

Cup Circuit mode cups

Successfully complete the easy, medium, and hard challenges in the indicated zone in Challenge mode to unlock the corresponding Cup Circuit mode cup:
Blue Chaos Cup: Death Yard Zone
Cyan Chaos Cup: Colosseum Highway Zone
Green Chaos Cup: Forest Falls Zone
Grey Chaos Cup: Complete every challenge in the game
Purple Chaos Cup: Meteor Base Zone
Red Chaos Cup: Sky Park Zone
Yellow Chaos Cup: Crystal Mountain Zone