Speak to Specialist Traynor after speaking to EDI to be made aware of a new mission to help some students trapped in the Petra Nebula ** galaxy at the Grissom Academy (it’s well highlighted when you enter the solar system).
Onboard the Ship
Once you’re on board, move forwards and immediately after opening the doors in front of you, take cover and mow down the regular Cerebus troopers trying to enter the door to your ally. Enter the door and after the cut-scene run through the door, grab any ammo you need off of the sofa and then go right.
Slide over the broken window to your right and up near the top of the steps you’ll find the Assault Rifle Stability Damper . Snap it up before entering the next room where you’ll see two troopers with their backs to you speaking to someone inside a barrier. Set one of your colleagues powers on one of them as you take down the other trooper, speak to Reiley where you’ll hear about his sister that needs rescuing also.
Slide over the nearby window and on a desk to your immediate left there’s a terminal you can scan for 20XP . On a different desk in here there’s a SMG Heat Sink for you to collect, so grab it and head out through the door at the top of the room.
Entering the next room is a prelude to an impending battle as multiple Centurion and Assault Troopers will enter the same room, allowing you to ambush them. The first enemies will arrive through the left-hand door, so line yourself up behind cover on the right, giving you an excellent view to kill and set the fight off in earnest.
If your sniper rifle has been equipped with a second level scope, it’ll allow you to see through the smoke field, otherwise, look for the red boxes signifying they’re there and hit them with biotic powers and your trusty guns.
Once they’re all dead, walk through the left-hand door and resting on a nearby seat you’ll find the - highly effective - M22 Eviscerator Shotgun (it has a crazy amount of damage). Now go through the door opposite and also resting on a seat (look for the seats straight ahead of you) on the right is some ammo and another new gun, the impressive M-96 Mattock Assault Rifle .
Look around the left corner and on the seat there’s the Mnemonic Visor along with Reiley’s sister, Seanne who you can talk to and rescue for 100 XP and +5 Reputation points . A locker behind you wields 1,350 Credits if you scan it.
Now make your way towards the Orion Hall where you’ll receive a message about the trapped students. After opening the second door you’ll trigger a cutscene where you’ll be up close and personal with a Cerberus Atlas Mech!
Orion Hall Atlas Battle
Unless you’ve played the ‘From Ashes’ DLC already, this’ll be your first time up against an Atlas Mech. Ideally you’ll have some grenades on you (preferably sticky ones), and if you’ve spoken to Garrus on the Normandy, you would have done well to have equipped the Armor Piercing skill in the med-bay beforehand (as the additional damage to the Atlas’s armor is worthwhile having for players who use their guns more than biotic powers).
Take cover behind the nearby seats and lob all of your grenades right at it to soften it up substantially. If you’ve any armor destroying powers, now’s a perfect time to use them! Infiltrators can use the cloak to simply create a 40% damage boost for their sniper rifle (as witnessed in the video), otherwise combo your team’s non-biotic powers directly onto it.
If you don’t have a sniper rifle, then try and get behind it and blast out the vulnerable back end with the most powerful weapon you have (so flank it if your allies are keeping it distracted). Once it’s destroyed, focus your attentions on the Assault and Centurion troopers that come out of either the left or right-hand upper doorways. Biotic powers will work wonders on these foot soldiers.
To the Atrium
Time to pick up a few valuables before moving on to the next encounter. Look at the seats, on either side of the room, where there’s a Medi-Kit for 100XP and any gel if you need it, and at the opposite side there’s a datalog worth 20 XP beside the camera controls you’ve been asked to activate.
With the camera feeds done, your next task is to find the door override, so head up the stairs to where the students are and look for a computer you can scan on the right wall, powering up the door to the atrium directly below (granting you a sweet 500 XP bonus in the process).
Before you go though, be sure to pick up the Assault Rifle Precision Scope and 1,875 Credits from a datapad on a table. When you open the door below, you’ll be given a choice: choosing the safer option will earn you Paragon points, whilst telling the students to risk it will earn you Renegade points.
When entering the courtyard, make a dash immediately to the right-hand side and run halfway up the ramp. You’ll gain an immediate height advantage but watch out for the Engineer to your right (near the stairs) and keep a close eye to your left for any guards trying to flank you - two Guardians will show up to your right near the defence generator.
Keep your allies close to you and as most of the enemies appear around the defence generator directly below you, you can get the drop on them before they even get the chance to see you. Keep checking your sides and using any biotic powers.
Ignore the Atlas on the other side for now and instead keep focused on just killing all of the foot soldiers first. After a couple of waves, drop down and then focus your attention purely on the Atlas Mech from the lower level. Snipe/focus your destructive powers on the cockpit to deal maximum damage with every attack. A minute or two of concentrated fire will see it go down. Enter the doorway on your right for a Medi-Kit , ammo and 3,750 Credits on the nearby chairs.
This time you start on the lower field, giving the Cerberus troops the height advantage. Firstly look into the far corner for the Engineer trying to set up a turret; deal with him as a priority, then look for a second Engineer on the right (also attempting to set up a turret). Only once these guys are dead should you focus on the Centurions and Assault Troopers.
Be wary as well of the enemies above you; two Guardians will attempt to flank you via the stairs behind you, so head them off with biotic powers or a rifle bullet to their faces. There will be more Engineers on the upper level, so get up there and drop them before they’re able to build any of those - rather annoying - turrets. Keep the pressure up and once they’re all dead, grab any ammo laying around and head into the open door on the lower floor.
Save the Students and Reach the Ship
Opening the next door leads into a T-shaped corridor where on the left you’ll see two guards attempting to intimidate two students protected by a shield. Set an ally on one as you kill his colleague beside him, but before you approach the students, turn around and scan the nearby terminal for an easy 4,375 Credits .
Walk up to the students and you can either earn Paragon or Renegade points depending on how you answer their questions. Go through the door to your right and in the next room there’s a terminal with the Schematics for a Biotic Amp that should be picked up as it’s key to an optional side-mission in the Citadel.
Immediately after opening the nearby door, slide over the blockage and on a chair to your left there’s the Serrice Council Chestplate armor. Just behind the next door there’s an Engineer guard with his back to you; if you kill him before he sees you, you can steal his Atlas Mech and use it for yourself!
The Mech can take some serious punishment and you have a long range rifle and a short range melee attack to hand. To be honest, ignore the melee attack and instead focus on using the gun as it can kill all troopers in a single shot. Also, by knowing where the enemies appear (it’s a set pattern), you can gun them down before they even know you’re there! The first wave of Cerberus troopers are running around at the front of the hall below where the students are located. Easy pickings to start off with.
Immediately after dropping the last one, turn around 180 degrees, walk back to the other end of the hall and look for the door opening up and to your left. You can simply wait for the troopers to drop down, giving you loads of time to line up where they are and rip them apart with ease. As soon as all of these guys are down, look to your right for more of the same, and the same tactic applies; wait for them to land on the ground and off them with relative ease.
Guardian Troopers now show up behind you and from a doorway on your right, see to them ASAP and after they die look up and left at a doorway. These guys literally run at you in single file allowing you to fire at them like it was a carnival shooting game; easy stuff. Now turn around 180 degrees again and look at the left corner, to see more guys drop down from the ceiling; kill them then look to your right for the final batch of regular troops.
Now you must look to the right (the stairs where you came from) and another Atlas Mech will show up! As long as you still have your own Mech (and by following these steps, you really should have), simply aim your cannon at the cockpit and a few direct hits will see it drop.
Once you hear the “All Clear!” over the intercom, step out of the Atlas and/or run to the top corner door that you can open. Running in here will trigger a cutscene that signifies the end of this mission.