Full list of all 700 Halo: The Master Chief Collection achievements worth 7,000 gamerscore.
The base game contains 400 achievements worth 4,000 Gamerscore, and there are 6 DLC packs containing 300 achievements worth 3,000 Gamerscore.
Halo 2: Spot the developer in the opening cutscene of Gravemind on Legendary in Classic Mode.