Sonic Rivals Codes -

Metal Sonic:
Successfully complete the game as Sonic, Knuckles, Silver, and Shadow.

Alternately, collect the "Metal Madness", "Metal Overlord", and "Neo Metal Sonic" cards.

Menu skins:
Successfully complete story mode as Knuckles, Metal Sonic, Shadow, Silver, or Sonic to unlock the corresponding menu skin.

Knuckles' leather shoes:
To get Knuckles' leather shoes, get Coconut 2002, Turtloids 2002, and Buzzer 2002.

Shadow's flame suit:
Get the cards Team Sonic, Team Rose, and Team Dark.

Silver's leather shoes:
To get Silver's leather shoes, get the card Chaos 2 (1998), Chaos 4 (1998), and Chaos 6 (1998).

Sonic's ice suit:
To get Sonic's ice suit you must have Miles "Tails" Power 2004, 2005, and 2002.

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

Cup Circuit mode cups:
Successfully complete the easy, medium, and hard challenges in the indicated zones 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