Okay so first I want to confirm that you do NOT get the mask when you beat the campaign on any difficulty. I guess you could say that there are two Ghosts mask, one is Ghost's mask from MW2 and the other is the Ghosts mask from Campaign. Now I'm pretty sure you get the MW2 Ghost mask from preorder or Hardened edition. But the Ghosts mask from campaign can be unlocked when you buy the Season Pass. So there you have it guys! Have fun with the last day of Double XP!