In Portal 2 for the Xbox 360, there are several items you can unlock for your Avatar by completing certain tasks.
Companion Cube Accessory – Complete the Single Player story
Love Shirt – Hug three friends in Coop mode
Portal 2 Hat – Survive the manual override
Portal 2 Shirt – Complete the Coop story
Turret Shirt – Complete Test Chamber 10 in under 70 seconds
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