That Just Happened

That Just Happened is an achievement in Halo: Combat Evolved Anniversary and Halo: The Master Chief Collection. It is awarded for completing The Library without dying on Heroic difficulty or higher. In the original game the achievement is represented by a skull on top of a purple octagon; in The Master Chief Collection it is represented by a screenshot of Infinity (strangely, sharing its image with the Close Quarters Combat achievement).

The achievement is worth 10 Gamerscore.

Tips

 * If you managed to unlock the Bandanna Skull, this is the best time to have the skull activated, as it will provide unlimited ammunition.
 * If you find yourself in trouble, don't be afraid to revert to your last checkpoint. Reverts do not count as deaths, and will not void your progress.
 * Try to run forward to trigger the Flood to spawn, then quickly retreat to cut down the forces as they approach. Also, repeat the method several times because the waves will be ready respawn the moment that the last wave is wiped out.
 * Always make sure your weapons are loaded.
 * It is recommended to carry a pistol and a shotgun as your weapons.
 * If you find an Overshield, take it.
 * Whenever you reach the elevators, avoid confronting the approaching enemies and run to the elevator.
 * Never kill a Combat Form that is armed with a Rocket Launcher at close range. If they are killed while still armed with the launcher they will fire one rocket at the ground or wherever their arm is pointed before collapsing onto the ground, engulfing everyone and everything around it.
 * If you have the mythic skull unlocked, activate it during this level. It will bolster the shields of your allied Sentinels and has no effect on the Flood.

Trivia
The Achievement's name is a direct quote made by Marine NPCs in Halo 3: "Yeah, that just happened!" which, in turn, is a reference to the film Talladega Nights: The Ballad of Ricky Bobby.