The Harlequin outfit in AC Brotherhood Xbox 360 cannot be unlocked today.
1. Earn Uplay units in-game (actions, completion). 2. Open Uplay overlay (Shift+F2 PC / Guide button console). 3. Spend ~20 units on "Harlequin" reward. 4. Sync → outfit in wardrobe.
For current AC, play Valhalla/Mirage on modern platforms with active reward ecosystems.