Priority: The Citadel 2 is the first mission of the second Mass Effect 3 act. The main mission is named Priority: The Citadel, but in order to avoid a possible confusion between this one and the third mission featured in the prologue, we will refer to it as Priority: The Citadel 2.
Unlike other Mass Effect 3 missions, Priority: The Citadel 2 begins directly after Priority: Tuchanka.
In other words, after you complete Priority: Tuchanka, if you wish to visit the Citadel, you will automatically start the second act of the game, and its first mission: Priority: The Citadel 2.
Because of this, it is very important to finish as many side-missions and Citadel quests as you can, before Priority: Tuchanka, otherwise you will not be able to find some characters required to complete them (for example, Barla Von).
The following Mass Effect 3 Walkthrough Act 2 Priority: The Citadel explains how to complete this mission in order to advance in the game.
The game guide offers useful tips that can help gamers to acquire more weapon mods, and to increase the amount of credits, allowing them to purchase additional items.
Priority: The Citadel 2 starts with a cutscene, which begins when you try to enter the Citadel. You will find that the Cerberus attacked the location assuming control over it.
After the cutscene, customize your team and weapons. For this mission, it is a good idea to play with Liara and Garrus/James.
When the mission starts you will enter the battlefield. Clear the area, and take out the Combat Engineers first, to stop them from deploying turrets. Push forward towards Commander Bailey and talk to him, then continue through the door in his office.
Move forward and take out all Cerberus on your way to the Executors Office. Follow the stairs to the left and when you reach the lobby, check the right side, and on the desk you should find a Med Kit and the Assault Rifle Piercing Mod.
Dont forget to check the Terminal and the C-Sec Officers corpse.
Next, bypass the door and advance until you reach a chamber where the fire extinguishing systems started. After you completely clear the area, check the door to the left, near the entrance, because behind it you will find the M-76 Revenant (near the first sink) and 6250 Credits inside a locker.
Now, exit and check the table to the left, for the Recon Hood, and the exit door for a Medical Station. On your way out, snipe the Engineer to the left and go through the broken windows.
On a shelf you will find the Sniper Rifle Extended Barrel and near it a Weapon Bench. Between them shoot the latch then activate the elevator. Use the elevator to reach the next area.
Now, follow the corridor and search the first room to the right for the Pistol Piercing Mod, and the one to the left.
Near the locked door, to the right is a small chamber where you will find the Securitel Helmet and the Pistol High Caliber Barrel Mod.
Return to the main corridor and look for a corpse carrying the M-25 Hornet SMG. Use the chamber to the right to advance, and eventually you will enter a long corridor.
If you search the first room to the right, you will find another Medical Station, and on the sink, to the right, some credits. Continue to advance and take out the Cerberus Centurions that spawn on the other side.
After you kill them, search their spawning point for Sniper Rifle Piercing Mod and a Medical Station.
Follow the stairs up and when you open the next door, you will enter the Executors Office. Watch all cutscenes showing Kai Leng, and get ready because when the cutscene ends you will have to take out several Nemesis and Phantoms.
The latter should be killed immediately from cover, because these snipers deal increased damage. Regarding the Nemesis, they are weaker and can be executed with several well-placed head-shots.
Advance toward Shalmar Plaza, and jump over the gap. Continue until you reach a blocked door. Jump through the broken window to the right, then jump down on the balcony, and head through the tunnel located to the left. Some credits (on a crate to the left) can be salvaged before jumping down in the next area.
Now, take out the Cerberus controlling the Atlas Mech (Hijacker Achievement/Trophy) , then use the robot to kill the remaining Cerberus forces. Follow the stairs on the left side of the plaza, and open the next door.
During the next phase you will be on top of an elevator.
Make sure you hit the Power Conduits under the elevator that appears to your right, then take out the Phantoms that spawn to the left. Repeat this step again and jump on the elevator to the left. Bailey will inform you when to do so.
In the final cutscene, you will have to make another important decision. If you play it as a Renegade, Udina dies by your hand. Additionally, Ashley or Kaidan may die, if, during the game, you played as a Renegade while talking to them.
Choose your answers wisely. Our decision was to continue to increase our Paragon rating, and Udina died killed by Kaidan.
After the final dialogue, you will have to return to Normandy. On your way, you can add Ashley or Kaidan to your crew.