In Sonic the Hedgehog 4: Episode 1 for the Xbox 360, you can unlock a full Sonic avatar costume.
The Sonic costume comes in two different pieces. There is a head piece, and a body piece.
To get the Sonic head piece, you’ll need to collect all rings at the end of the final stage.
To get the Sonic body piece, you’ll need to collect all seven Chaos Emeralds from the Bonus Stage in each level. To access the Bonus Stage in a level, you’ll need to collect 50 rings in that level, which will make a giant ring appear at the end of the level. Jump into the giant ring and you’ll access the Bonus Stage, and a Chaos Emerald will be at the end.
