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To obtain this achievement you must finish all levels meeting par times. I will give the amount of time for each mission required and a video on how to do it. Do note all videos are done on easy and that it is possible you can unlock the achievements going for Par Scores, or the Goat Roped achievement which you need to beat Halo: CE in under 3 hours total on legendary difficulty:
If you want to do those first you can choose from the list the video that you need and which mission it is. Or if you want to knock them out of the way or don't plan on doing the other achievements just start from the list going down.
Note: Videos were done by MrInfamouzgaming
The Pillar Of Autumn Par time: 15 minutes (done in 8:38)
Halo Par time: 20 minutes (done in 18:42)
The Truth and Reconciliation par time: 20 minutes (which is done in 17:27)
The Silent Cartographer par time: 15 minutes (video was done by Korbek gaming which will also unlock you the pacifist achievement)
Assault on the control room par time: 15 minutes (done in 14:18)
343 Guilty Spark par time: 15 minutes (done in 9:04)
The Library par time: 25 minutes (done in 15:28)
Two Betrayals par time: 20 minutes (done in 15:19)
Keyes par time: 15 minutes (done in 7:10)
The Maw par time: 15 minutes (done in 7:43 by Mater, you will also obtain the "This side up" achievement if you don't flip your vehicle)