The Guardians Are Coming
From Halopedia, the Halo wiki
The Guardians Are Coming is an achievement in Halo: The Master Chief Collection. It is unlocked by getting killed in a manner which is unrecognizable for the game engine.
This achievement can be unlocked through many means. For example, getting killed by environmental objects (such as Halo 2s Terminal train) or scripted objects (like turrets on Halo 3s Snowbound) will unlock this achievement.
Trivia
- This is a pun referring to Halo 5: Guardians.