How does rank work in Halo 3?

In Halo 3s multiplayer matchmaking system, there are two types of ranks. The Global Rank is shown on the Service Record and is based upon a combination of the players highest ranked skill level and total number of Experience Points (EXP).

How do you rank up in Halo?

To rank up youll need XP, and the two places to get them are multiplayer and Firefight. Once you have some season points youll be able to spend them on various cosmetics. Youll have to unlock them in sequence, however, so youll need to work a bit for the bits of gear that you want.

How do you get a haunted helmet in MCC?

Its a Tier 100 reward, it unlocks once you use your last Season Point. Its under the Pilot helmet type.