Praetorian

A Praetorian is a slow-moving flying Collector construction which appears in Mass Effect 2. It consists of thirty deformed Husks fused together, and has a strong barrier and powerful armor (acting as its health), giving it high durability. The Praetorian is encountered on three occassions, at the end of the mission on Horizon, during the escape from the Collector Cruiser, and during the attack on the Normandy SR-2.

Capabilities
Offensive

The Praetorian attacks in two different ways:
 * Particle Beams: When the Praetorian is hovering and has a clear shot, it will fire its particle beam towards its opponent for about 3 seconds, followed by 2.5 seconds of cool-down time. It only takes a couple of seconds of exposure to this weapon to kill Shepard.


 * Death Choir: A ground attack followed by an area effect attack: first, the ground strike knocks the Praetorian's opponent back for about a second. After that, there is only a short period of time left to run away from the area-effect attack, which is likely to cause an instant death. The ground strike is triggered if an opponent is within range of the attack or if the Praetorian's barrier is depleted and its armor has taken a threshold amount of damage (typically when its armor reaches 3/4, 1/2 or 1/4 strength). Note: The Praetorian is invulnerable during this attack. After the attack is complete, its barrier will be fully recharged.

Defensive

The Praetorian has extremely strong armor. At first sight it has no barrier, but the Death Choir gives it a biotic barrier, which recharged after each Death Choir attack.

General Tactics
Before the fight, be sure to equip all of your weapons (the shotgun isn't as important, but if you run out of ammo for everything else, it can still be useful) with Armor Piercing Ammo, Warp Ammo, or Incendiary Ammo, if available. Warp Ammo is ideal, but Armor Piercing Ammo is preferable to Incendiary. If you have both Warp Ammo and one of the others, equip half of your weapons with each, using Warp ammo on the Praetorian's barrier and the other type when its armor is exposed after you run out of Collector Particle Beam (CPB) ammo. The M-9 Tempest SMG is particularly effective at dealing with the Praetorian's barrier, as it can be used at medium to medium-long ranges on full-auto due to the Praetorian's large profile.

During the actual fight, Shepard appears to be the only opponent the Praetorian follows and the only target of its particle beam. However, your squadmates can trigger the ground-strike attack. The Praetorian will constantly move towards Shepard, apparently trying to find a chance to use its ground-strike attack. During this fight, it is ESSENTIAL to keep mobile. Take cover when you can, as it will protect you from the particle beam attack, but if the Praetorian gets near enough to use its ground-strike attack, you'll be in a very sticky situation. Your team-mates' location isn't really important, just set them both to attack the Praetorian and use Unity whenever they "die". Use your CPB until you run out of ammo, then any of your other weapons following the ammo suggestions above.

Class Specific Tactics
As a Soldier, equip yourself with the M-920 Cain because on insanity difficulty a hit will leave the Praetorian with 25% armor, but by the time you get your senses back, it will have restored its barrier. Use Concussive Shots to deal with the barrier and a Widow sniper rifle with Incendiary Ammo will deal very decent damage to its armour as well. Try to stay as far away from the Praetorian as possible and snipe or use Concussion Shot on it as quickly as possible. Once the barrier is down, use Adrenaline Bursts to get as many shots in as possible. Incendiary Ammo is useful once the barrier is down. If you keep your distance and make sure to keep your squad out of the ground attack's range, the fight should be over pretty quickly. If you see the Praetorian getting too close, use an Adrenaline Boost to get away. Having Garrus on board is also convenient, as his Concussive Shot helps take down the barrier much quicker. Warp-wielding squadmates are also effective against barriers and armour. As a Sentinel or Adept, both of the Praetorian fights offer areas of the map that will allow you to circle behind objects to keep you permanently safe from the Praetorian. On Horizon, there is a truck in the top-right corner (from your entrance) that you can circle while launching Warp attacks around the truck, thus keeping you safe from the Praetorian while you and your team whittle down its barrier and armor. On the Collector Ship, there is a pillar off to the left side (from your entrace) that you can circle while launching Warp attacks around the pillar, again keeping you safe from the Praetorian. While neither off these tactics end the fight particularly quickly (you might want to use the Cain first), they will keep you safe as the Praetorian attempts to maneuver around these obstacles while allowing you launch attacks. As an Infiltrator, you have the ability to use Tactical Cloak to keep out of the Praetorian's sight, which will cause it to ignore you for a few seconds to focus on your squad. If one of your squadmates is on the other side of the battlefield, by the time your cloak runs out, the Praetorian will have given you plenty of room to maneuver and a clear shot as it turns around (especially useful on the Collector Ship if you chose the M-98 Specialization). Use Submachine Gun fire (preferably with Warp Ammo) to take out the Praetorian's barrier before following up with sniper fire or heavy weapons against its armor. Once the Praetorian is focused on you, your squadmates will have some time to recover before you reactivate Tactical Cloak and repeat the process. Essentially, you're playing ping-pong with your squadmates, using the Praetorian as the ball. This is best done with durable squadmates who have Concussive Shot, like Grunt or Zaeed, who can also deal with any other nearby enemies such as Husks or Collectors, but any squadmate will work if they have enough health and/or cover to survive a shot from the Praetorian's particle beams.
 * Conditions: Insanity, Soldier, M-98 Specialisation
 * Conditions: Insanity, Sentinel or Adept
 * Conditions: Insanity, Infiltrator

Trivia

 * The Praetorians are likely named after the Praetorian Guard, a force of bodyguards used by Roman Emperors until the fourth century AD.
 * The Praetorians can also engage their enemies in close combat, using sword-like extremities to tear them apart, which is shown during the attack on SR-2 Normandy.