Halo 3: Find and claim the Iron Skull.
Complete 300 missions or multiplayer games.
Complete any co-op level on Legendary difficulty.
Halo CE: Find and claim the Malfunction skull in remastered mode.
Halo CE: Complete The Library on Heroic or Legendary difficulty without dying.
Halo 2: Complete the level Regret with the Prophet Birthday Skull activated.
Halo 4: Survive Spartan Miller (Ep.5 Ch.1) of Spartan Ops on Heroic or Legendary.