That Just Happened

That Just Happened is an achievement in Halo: Combat Evolved Anniversary that is awarded for completing The Library without dying on Heroic difficulty or higher. It is represented by a skull on top of a purple octagon.

The Achievement is worth 10 Gamerpoints.

Tips

 * If you managed to unlock the Bandana Skull, this is the best time to have the skull activated. It will provide unlimited ammunition.
 * 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.
 * Try to always have a shotgun ready with either a pistol or plasma-based weapon as a secondary weapon.
 * If you find an Overshield, take it.
 * Whenever you reach the elevators, avoid confronting the approaching enemies and run to the elevator.
 * When playing in cooperative mode, if one of the players die, the player that manages to survive the entire level will be the only one to unlock achievement.
 * 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.

Trivia
The Achievement's name is a direct quote made by Marine NPCs in Halo 3: "Yeah, that just happened!"