That Just Happened

That Just Happened is an achievement in Halo: Combat Evolved Anniversary that is awarded for coompleting the level The Library without dying on Heroic or higher difficulty. It is worth 10 Gamerscore points.

It is represented by an skull which is surrounded by a purple octagon.

Trivia
The achievement is a reference to a quote made by Marine NPCs in Halo 3: "Yeah... that just happened!"