Complete Halo: The Master Chief Collection Armor Customization options for Halo: CE, Halo 2 Classic, Halo 2 Anniversary, Halo 3, and Halo 4. Including some popular sets of armor such as RECON, HAYABUSA, KATANA, FOTUS, and the Flaming Head!
In game look of Halo 2 Anniversary’s armor customization for Spartan and Elites: MARK VI, Centurion, Hoplite, Elite, Outrider, and Invader.
4 Unlockable Armor Sets for Halo 5: Guardians Multiplayer Beta were revealed. You can unlock these by earning achievements in Halo: The Master Chief Collection
Nightfall
Watch the Halo: Nightfall Episode 1 Second Story (Unlocks Helmet)
Watch all 5 episodes of Halo: Nightfall (Unlocks Armor) 
Mark VI
Earn the “Your Journey Begins” Achievement in MCC
Complete 1 match or mission 
Mark VI Scarred
Earn the “Cairo Station” Achievement in MCC
Play and beat the Cairo Station mission in Halo 2 Anniversary 
Helioskrill
Earn the “Legend” Achievement in MCC by completing all 4 campaigns on Legendary
Source: IGN
Chief Canuck - Video Game News 