In Halo Warsthere are collectible Black Boxes that add information to an in game timeline.
Allied AIs are allowed to trade weapons with players and drive them around in certain situations. Reacheach player plays as their customized Noble Six. I just noticed this in my RSS feeds, it looks like it will be coming out in a couple of weeks. In all other games, these skulls are automatically unlocked. The Arena matchmaking system focuses only on Slayer -related gametypes and is somewhat similar to Halo 2' s Optimatch option where players are able to alter their matchmaking settings by their preferred gametypes and playlist.