Assault on the Control Room
Halo Runs record page: http://www.haloruns.com/records?lb=105 (click the timestamps for video links)
It is possible to drop from the first bridge in the level to the canyon floor below, which breaks enemy spawn triggers for the rest of the level. Going through the rest of the level is trivial. The trick has 3 parts, 2 of which have alternate easy and difficult methods.
The positioning and movement for each drop is quite precise and is best presented in a video tutorial:
After you've successfully completed Bridge Fall, not only does it skip all enemy spawns, it also prevents a door later in the level from unlocking if you were to proceed normally. This is the reason you must grab the first banshee that sits aback the dead end canyon. Standing at the back of the canyon next to the banshee, look back toward where you came and look up. There are two bridges. The left end of the nearest bridge is the door you must fly to/enter to proceed.
There is one place later in the level where a grenade jump can save 5 or more seconds. In the first room after exiting the first banshee, as you enter the inner part of the room, you can do a single grenade jump up to the platform on your left. An example video can be seen here.