Complete thse task's to unlock avatar rewards for halo.

Carter's Helmet - Clear a Campaign mission on Legendary without dying (Note: To get this easily, play through an entire level on Legendary and die as much as you want. At the end of the level, savea nd quit. Choose "Resume Campaign" and then finish the level without dying to get the Avatar.)

Emile's Helmet - Earn a Bulltrue medal in either multiplayer or Firefight Matchmaking (Kill someone while they're lunging with an Energy Sword attack)

Jorge's Helmet - Earn a Killtacular in multiplayer Matchmaking (Kill 5 enemies within 4 seconds of eachother)

Jun's Helmet - Kill 100 enemies in a row without dying in either the Campaign or Firefight (set your shields/life to infinite in a Firefight match)

Kat's Helmet - Avenge a teammate's death in multiplayer Matchmaking (Kill someone who killed your teammate)