The Hangar: When you make it there you want to slide jump down the stairs, because there's a really subtle trigger that spawns the 1st set of phantoms. There's a full BR in the basement of the hangar, if you happen to run out of ammo while dealing with the phantoms.
FIGHTING STRATS GO HERE
While you're walking out of the hangar you can do a launch off of one of the cones in the hallway (NEEDS A PICTURE OF THE CONE)
Drone Fight: If you have any sticky nades when you make it to the drone fight you can use them to kill the drones that pick up the marine, because they can sometimes not get killed by any marines. To kill the drones coming out of the pipe you just aim slighty under the pipe with the turret at the left side of the room.
After you kill all the drones you want to get a plasma pistol(or have acquired one beforehand) so you can weaken the brute chieftain in the next section, and after doing so you can just br him to death for his gravity hammer, just make sure you don't have any equipment, because he will drop a flare, and you can maybe accidentally pick it up instead of the hammer.
The 2 Hammer launches: After dropping down the shaft you want to crouch on the edge of the grate on the ground not facing wall and after the cortana moment is over you want to drop a nade so it lands against the wall so it's set up for a launch. You can do a hammer launch on your jump up, but there's a way smaller chance to die by hitting a wall by just doing it on your way down.
When you get to the area with the big chasm, you want hit the door so that the pelican will load on the landing pad. After hitting the door you want to a hammer launch off the grate on the wall so you skip the entire brute section. Then you go hit the elevator button, and then jump on top of the light on the wall and then into the elevator, so you don't have to wait for the door to open(the elevator won't crush you).
Landing pad fight: For the landing pad fight you want to kill 2 brutes and then jump on top of the pelican so you can get up to the top where 5 brutes will spawn. After you kill 5 brutes the door on the right side of the area will open with 4 additional brutes for you to kill. When all the brutes are dead you want to drop down to the fusion coil that is close to the door and set it up for a launch off of it. An easy way to set it up is to throw a spike grenade on the wall behind it.
Escape: When you get past the cortana moment, you want to do a hammer launch off of the weapons case. Then after getting to the bomb room, you can do another launch off of a weapon case, which in an ideal scenario will get you right next to the bomb. When you get to the section where you did a DC lanch before you want to do a butterfly "jump" so you can ride one of the drones and finally, when you get to the hangar you want to launch off of the last weapon case and then enter the elevator to end the level.
Know Your Role...
There is not much to say here for legendary. Simply optimize movement and make sure to pick up a BR at the bottom of the staircase when exiting the first room.
Going fast in the first hallway fight hinges on good grenade throws and prioritizing the brute near the doorway to the next area. If he goes down quickly the surrounding grunts will panic and flee. You can use the slot in the barricade behind the first large shipping container to overcharge the brute.