Fast Fall Achievement in Halo: The Master Chief Collection

In order to beat the par time on each of the nine missions of Halo: Reach's Campaign, you will want to take two things into account. First, play on the Easy difficulty setting so that enemies aren't as dangerous. Second, utilizing the various speed running tactics as shown in the "Keep Your Foot on the Pedrogas" achievement will help immensely in skipping certain firefights and finishing each mission in a considerably less amount of time as normal. With these tips in mind, you should have no problem completing each mission under par time.

Overall, just remember to play on the lowest difficulty setting and try rushing past as many firefights (when possible). Once you beat the par time for all nine missions, this achievement will unlock.

NOTE: It is not absolutely required to play missions on Easy in order to beat their par time. In fact, some of these achievements can and may come naturally during any Legendary playthrough. If they don't, though, it's then easiest to just do them on Easy.